secrets-init: SERVICE_TOKEN читаемый для сервера (как DB_PASSWORD, JWT_SECRET)

Без этого после #26 сервер не стартует: AccessDeniedException /run/mail-secrets/SERVICE_TOKEN
(на prod поправлено руками chmod 644 в томе 2026-11-07).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -8,6 +8,21 @@
 
 **Регистрации нет:** ящики создаёт администратор `admin@jambocheck.com` — веб-почта → Настройки → **MAILBOXES**.
 
+**Ловушка у ящика (TRAP):** Настройки → MAILBOXES → кнопка `outbox` у ящика. Всё, что такой ящик отправляет (SMTP или веб) **на чужие адреса**, никому не доставляется: одна копия ложится в его же INBOX. Письма на наши адреса и рассылки (`alerts-staging@`) доставляются как обычно. Для `staging@` — тестовые письма staging-стенда не попадают к живым людям, а алерты staging доходят до команды.
+
+**Папки по `+метке`:** письмо на `bob+prod@jambocheck.com` ложится в ящик `bob@` в папку **prod** (создаётся сама). В имени ящика и рассылки `+` нельзя. Метка не может быть системной папкой (Spam, Trash …) — тогда INBOX.
+
+**Рассылки (LISTS):** Настройки → LISTS. Письмо на адрес рассылки (`alerts-prod@`) → **каждому участнику своя копия** (своё «прочитано») в папку рассылки. Закрытая рассылка (по умолчанию) принимает письма только от вошедших отправителей (Kuma через `monitor@`, Jambotron) — снаружи 550. Адрес рассылки не может совпадать с ящиком.
+
+**Несколько ящиков у одного логина:** слева в меню **MAILBOXES** — свой ящик, общие, в которых ты участник, и подключённые (кнопка ⊕: адрес + пароль того ящика). Клик — переключиться; «×» — убрать из своего меню.
+
+**Общий ящик** (`support@`, `billing@`): Настройки → MAILBOXES → галочка «shared mailbox» при создании, кнопка `group` — кто может его открывать. Своего пароля и входа у него нет; «прочитано» общее (командный ящик); у письма видно **«Answered by …»** — кто ответил из веб-почты. В профиле открытого чужого ящика пароль/имя не меняются.
+
+**В почтовой программе** (Thunderbird, телефон) общий или подключённый ящик — логин `ящик*свой_логин` (например `support@jambocheck.com*jambotronpw@jambocheck.com`) и **свой** пароль; так и для IMAP, и для SMTP (письма уходят от имени общего ящика).
+
+**Служебное API для Jambotron** (`/api/service/**`, заголовок `Authorization: Bearer <SERVICE_TOKEN>`; токен генерирует `secrets-init` в томе секретов — файл `SERVICE_TOKEN`, без токена API выключено): Общие ящики: `PUT /shared/{address}` `{displayName, members[]}` — создать при отсутствии, точный состав участников; выключение аккаунта убирает его и из общих ящиков.
+`PUT /accounts/{email}` `{displayName, active}` — создать (201 + пароль один раз) или изменить; `active:false` — выключить и убрать из всех рассылок · `POST /accounts/{email}/password` — новый пароль один раз · `GET /accounts/{email}` · `GET /lists` · `PUT /lists/{address}` `{folder, description, openToOutside, members[]}` — точный состав · `DELETE /lists/{address}`.
+
 **Администратор:** `admin@jambocheck.com`, пароль `eK-6oj3TMtZgoXVxlvtCWFI6` (начальный, записан 2026-11-07 по решению владельца; сменили — обновить здесь).
 
 Пароли остальных ящиков (`staging@`, `no-reply@`, `monitor@`) — в репозитории Jambotron: `INFRASTRUCTURE/SECRETS.md`, раздел «Почта mail.jambocheck.com».

backend/src/main/java/com/mailserver/config/ImapConfig.java

@@ -27,8 +27,9 @@ public class ImapConfig {
     @Bean
     public ImapStore imapStore(DatabaseClient db, UserRepository users, UserService userService, MailService mailService,
                                MessageRepository messages, AttachmentRepository attachments, MessageSources sources,
-                               @Value("${mailserver.smtp.hostname:localhost}") String hostname) {
-        return new DbImapStore(db, users, userService, mailService, messages, attachments, sources, hostname);
+                               @Value("${mailserver.smtp.hostname:localhost}") String hostname,
+                               com.mailserver.service.MailboxAccess access) {
+        return new DbImapStore(db, users, userService, mailService, messages, attachments, sources, hostname, access);
     }
 
     @Bean(initMethod = "start", destroyMethod = "stop")

backend/src/main/java/com/mailserver/config/MailDomains.java

@@ -44,6 +44,24 @@ public class MailDomains {
         return domains;
     }
 
+    /**
+     * Address without its "+tag": {@code bob+prod@x} → {@code bob@x}. Mailbox and list names never contain "+",
+     * so the part after it is a label chosen by the sender — the folder the message goes to.
+     */
+    public static String baseOf(String address) {
+        String lower = address.toLowerCase(Locale.ROOT);
+        int at = lower.lastIndexOf('@');
+        int plus = lower.indexOf('+');
+        return plus > 0 && plus < at ? lower.substring(0, plus) + lower.substring(at) : lower;
+    }
+
+    /** The "+tag" of an address, or null: {@code bob+prod@x} → {@code prod}. */
+    public static String tagOf(String address) {
+        int at = address.lastIndexOf('@');
+        int plus = address.indexOf('+');
+        return plus > 0 && plus < at - 1 ? address.substring(plus + 1, at) : null;
+    }
+
     public static String domainOf(String address) {
         int at = address == null ? -1 : address.lastIndexOf('@');
         return at < 0 ? "" : address.substring(at + 1).toLowerCase(Locale.ROOT);

backend/src/main/java/com/mailserver/config/SecurityConfig.java

@@ -52,6 +52,8 @@ public class SecurityConfig {
             .cors(cors -> cors.configurationSource(corsConfigurationSource()))
             .authorizeExchange(exchange -> exchange
                 .pathMatchers("/api/login", "/api/register", "/api/config", "/actuator/health").permitAll()
+                // service API for Jambotron: its own token, checked by ServiceController (not a mailbox login)
+                .pathMatchers("/api/service/**").permitAll()
                 .pathMatchers("/api/**", "/actuator/**").authenticated()
                 // the web client (static files, SPA routes)
                 .anyExchange().permitAll()

backend/src/main/java/com/mailserver/controller/AuthenticationController.java

@@ -99,6 +99,10 @@ public class AuthenticationController {
                         return delay.isZero() ? answer : answer.delayElement(delay);
                     }
                     guard.success(ip, email);
+                    if (user.isShared()) {
+                        return Mono.just(ResponseEntity.badRequest().body(Map.of("error",
+                                "This is a shared mailbox: log in with your own mailbox and open it there")));
+                    }
                     if (!user.isActive()) {
                         return Mono.just(ResponseEntity.badRequest().body(Map.of("error", "User is deactivated")));
                     }
@@ -138,7 +142,7 @@ public class AuthenticationController {
 
     @PutMapping("/me")
     public Mono<ProfileResponse> updateMe(Mono<Authentication> auth, @Valid @RequestBody Mono<ProfileUpdateRequest> body) {
-        return user(auth).zipWith(body)
+        return own(auth).zipWith(body)
                 .flatMap(pair -> userService.updateDisplayName(pair.getT1(), pair.getT2().displayName()))
                 .flatMap(this::profile);
     }
@@ -147,7 +151,7 @@ public class AuthenticationController {
     public Mono<Map<String, String>> changePassword(Mono<Authentication> auth, @Valid @RequestBody Mono<PasswordChangeRequest> body,
                                                     ServerHttpRequest http) {
         String ip = clientIp(http);
-        return user(auth).zipWith(body)
+        return own(auth).zipWith(body)
                 .flatMap(pair -> {
                     User user = pair.getT1();
                     // Someone with a stolen session must not guess the current password either
@@ -186,6 +190,15 @@ public class AuthenticationController {
                         admins.isAdmin(user.getEmail())));
     }
 
+    /** The session's own mailbox — not a shared / attached / administrator-opened one: no profile changes there. */
+    private Mono<User> own(Mono<Authentication> auth) {
+        return auth.switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.UNAUTHORIZED)))
+                .flatMap(a -> com.mailserver.security.Actor.opened(a)
+                        ? Mono.error(new ResponseStatusException(HttpStatus.FORBIDDEN,
+                                "This mailbox is opened from " + com.mailserver.security.Actor.login(a) + " — change it in Settings → MAILBOXES"))
+                        : user(Mono.just(a)));
+    }
+
     private Mono<User> user(Mono<Authentication> auth) {
         return auth.switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.UNAUTHORIZED)))
                 .flatMap(a -> userService.findByEmail(a.getName()))

backend/src/main/java/com/mailserver/controller/MailController.java

@@ -150,7 +150,8 @@ public class MailController {
     @PostMapping("/send")
     public Mono<MessageResponse> sendMessage(Mono<Authentication> auth, @Valid @RequestBody Mono<SendRequest> requestMono) {
         return auth.zipWith(requestMono)
-                .flatMap(pair -> submissionService.send(pair.getT1().getName(), pair.getT2()));
+                .flatMap(pair -> submissionService.send(pair.getT1().getName(),
+                        com.mailserver.security.Actor.login(pair.getT1()), pair.getT2()));
     }
 
     // --- Drafts ---

backend/src/main/java/com/mailserver/controller/MailboxAdminController.java

@@ -4,6 +4,9 @@ import com.mailserver.config.MailAdmins;
 import com.mailserver.config.MailDomains;
 import com.mailserver.domain.User;
 import com.mailserver.dto.LoginResponse;
+import com.mailserver.service.MailDirectory;
+import com.mailserver.service.MailLists;
+import com.mailserver.service.MailboxAccess;
 import com.mailserver.service.MailService;
 import com.mailserver.service.UserService;
 import com.mailserver.util.JwtUtils;
@@ -13,6 +16,7 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.http.HttpStatus;
 import org.springframework.security.core.Authentication;
+import org.springframework.web.bind.annotation.DeleteMapping;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.PostMapping;
@@ -25,12 +29,9 @@ import org.springframework.web.server.ResponseStatusException;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
-import java.security.SecureRandom;
 import java.time.Instant;
-import java.util.Base64;
 import java.util.Comparator;
-import java.util.Locale;
-import java.util.regex.Pattern;
+import java.util.List;
 
 /**
  * Mailboxes of this server for its administrators ({@link MailAdmins}): list, create (no-reply@, monitor@,
@@ -42,16 +43,16 @@ import java.util.regex.Pattern;
 public class MailboxAdminController {
 
     private static final Logger log = LoggerFactory.getLogger(MailboxAdminController.class);
-    private static final Pattern LOCAL_PART = Pattern.compile("[a-z0-9](?:[a-z0-9._+-]{0,62}[a-z0-9])?");
-    private static final int MIN_PASSWORD = 10;
+    private static final int MIN_PASSWORD = MailDirectory.MIN_PASSWORD;
 
-    public record MailboxView(Long id, String email, String displayName, boolean active, boolean admin,
-                              long usedBytes, long quotaBytes, Instant createdAt) {
+    public record MailboxView(Long id, String email, String displayName, boolean active, boolean admin, boolean trap,
+                              boolean shared, List<String> members, long usedBytes, long quotaBytes, Instant createdAt) {
     }
 
     /** @param password empty — the server generates one and returns it once */
+    /** @param shared shared mailbox (support@): no login of its own — members open it; password ignored */
     public record CreateRequest(@NotBlank @Size(max = 254) String email, @Size(max = 100) String displayName,
-                                @Size(max = 200) String password) {
+                                @Size(max = 200) String password, Boolean shared) {
     }
 
     public record PasswordRequest(@Size(max = 200) String password) {
@@ -60,6 +61,9 @@ public class MailboxAdminController {
     public record ActiveRequest(boolean active) {
     }
 
+    public record TrapRequest(boolean trap) {
+    }
+
     /** @param password the generated password, or null when the administrator chose it */
     public record Created(MailboxView mailbox, String password) {
     }
@@ -69,9 +73,16 @@ public class MailboxAdminController {
     private final MailDomains domains;
     private final MailAdmins admins;
     private final JwtUtils jwt;
+    private final MailDirectory directory;
+    private final MailLists lists;
+    private final MailboxAccess access;
 
-    public MailboxAdminController(UserService users, MailService mail, MailDomains domains, MailAdmins admins, JwtUtils jwt) {
+    public MailboxAdminController(UserService users, MailService mail, MailDomains domains, MailAdmins admins, JwtUtils jwt,
+                                  MailDirectory directory, MailLists lists, MailboxAccess access) {
+        this.access = access;
         this.jwt = jwt;
+        this.directory = directory;
+        this.lists = lists;
         this.users = users;
         this.mail = mail;
         this.domains = domains;
@@ -89,24 +100,17 @@ public class MailboxAdminController {
     @ResponseStatus(HttpStatus.CREATED)
     public Mono<Created> create(Mono<Authentication> auth, @RequestBody Mono<CreateRequest> body) {
         return admin(auth).then(body).flatMap(request -> {
-            String email = request.email() == null ? "" : request.email().trim().toLowerCase(Locale.ROOT);
-            int at = email.lastIndexOf('@');
-            if (at <= 0 || !LOCAL_PART.matcher(email.substring(0, at)).matches()) {
-                return Mono.error(bad("Not a mailbox address: " + email));
-            }
-            if (!domains.isLocal(email)) {
-                return Mono.error(bad("Mailboxes can be created only in " + String.join(", ", domains.domains().stream().sorted().toList())));
-            }
             String chosen = request.password() == null ? "" : request.password();
             if (!chosen.isEmpty() && chosen.length() < MIN_PASSWORD) {
                 return Mono.error(bad("Password: at least " + MIN_PASSWORD + " characters, or leave it empty to generate one"));
             }
-            String password = chosen.isEmpty() ? randomPassword() : chosen;
-            return users.register(email, password, request.displayName())
-                    .onErrorMap(IllegalArgumentException.class, e -> new ResponseStatusException(HttpStatus.CONFLICT, "This mailbox already exists"))
-                    .doOnNext(user -> log.info("Mailbox created by administrator: {}", email))
+            boolean shared = Boolean.TRUE.equals(request.shared());
+            String password = chosen.isEmpty() || shared ? randomPassword() : chosen;
+            return directory.createMailbox(request.email(), request.displayName(), password)
+                    .flatMap(user -> shared ? users.setShared(user, true) : Mono.just(user))
+                    .doOnNext(user -> log.info("{} created by administrator: {}", shared ? "Shared mailbox" : "Mailbox", user.getEmail()))
                     .flatMap(this::view)
-                    .map(view -> new Created(view, chosen.isEmpty() ? password : null));
+                    .map(view -> new Created(view, chosen.isEmpty() && !shared ? password : null));
         });
     }
 
@@ -136,7 +140,7 @@ public class MailboxAdminController {
         return admin(auth).flatMap(me -> mailbox(id).map(user -> {
             log.warn("Administrator {} opened mailbox {}", me, user.getEmail());
             LoginResponse response = new LoginResponse();
-            response.setToken(jwt.generateToken(user.getEmail()));
+            response.setToken(jwt.generateToken(user.getEmail(), me));
             response.setEmail(user.getEmail());
             return response;
         }));
@@ -154,6 +158,57 @@ public class MailboxAdminController {
         }))).flatMap(this::view);
     }
 
+    /** Trap: what the mailbox sends is stored in its own INBOX, nothing leaves the server (staging@). */
+    @PutMapping("/{id}/trap")
+    public Mono<MailboxView> trap(Mono<Authentication> auth, @PathVariable Long id, @RequestBody Mono<TrapRequest> body) {
+        return admin(auth).flatMap(me -> body.flatMap(request -> mailbox(id).flatMap(user -> {
+            log.info("Mailbox {} trap {} by administrator {}", user.getEmail(), request.trap() ? "ON" : "OFF", me);
+            return users.setTrap(user, request.trap());
+        }))).flatMap(this::view);
+    }
+
+    public record MembersRequest(List<String> members) {
+    }
+
+    /** Exactly these members may open the mailbox (shared mailbox; for an ordinary one — delegates). */
+    @PutMapping("/{id}/members")
+    public Mono<MailboxView> members(Mono<Authentication> auth, @PathVariable Long id, @RequestBody Mono<MembersRequest> body) {
+        return admin(auth).flatMap(me -> body.flatMap(request -> mailbox(id).flatMap(user ->
+                directory.setMembers(user, request.members())
+                        .doOnSuccess(v -> log.info("Members of {} set by administrator {}: {}", user.getEmail(), me, request.members()))
+                        .then(users.byId(id)))))
+                .flatMap(this::view);
+    }
+
+    // --- Mailing lists (Settings → LISTS) ---
+
+    public record ListRequest(@Size(max = 50) String folder, @Size(max = 255) String description, boolean openToOutside,
+                              List<String> members) {
+    }
+
+    @GetMapping("/lists")
+    public Flux<MailLists.MailList> lists(Mono<Authentication> auth) {
+        return admin(auth).thenMany(lists.all());
+    }
+
+    /** Creates or replaces the list {@code address} (settings + the exact member set). */
+    @PutMapping("/lists/{address}")
+    public Mono<MailLists.MailList> saveList(Mono<Authentication> auth, @PathVariable String address,
+                                             @RequestBody Mono<ListRequest> body) {
+        return admin(auth).flatMap(me -> body.flatMap(request ->
+                directory.saveList(address, request.folder(), request.description(), request.openToOutside(), request.members())
+                        .doOnNext(list -> log.info("List {} saved by administrator {}: {} members", list.address(), me, list.members().size()))));
+    }
+
+    @DeleteMapping("/lists/{address}")
+    @ResponseStatus(HttpStatus.NO_CONTENT)
+    public Mono<Void> deleteList(Mono<Authentication> auth, @PathVariable String address) {
+        return admin(auth).flatMap(me -> lists.delete(address)
+                .flatMap(deleted -> deleted ? Mono.<Void>empty()
+                        : Mono.error(new ResponseStatusException(HttpStatus.NOT_FOUND, "List not found")))
+                .doOnSuccess(v -> log.info("List {} deleted by administrator {}", address, me)));
+    }
+
     private Mono<String> admin(Mono<Authentication> auth) {
         return auth.switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.UNAUTHORIZED)))
                 .map(Authentication::getName)
@@ -166,9 +221,9 @@ public class MailboxAdminController {
     }
 
     private Mono<MailboxView> view(User user) {
-        return mail.usedBytes(user.getId()).defaultIfEmpty(0L)
-                .map(used -> new MailboxView(user.getId(), user.getEmail(), user.getDisplayName(), user.isActive(),
-                        admins.isAdmin(user.getEmail()), used, user.getQuotaBytes() == null ? 0 : user.getQuotaBytes(),
+        return mail.usedBytes(user.getId()).defaultIfEmpty(0L).zipWith(access.members(user.getId()).collectList())
+                .map(pair -> new MailboxView(user.getId(), user.getEmail(), user.getDisplayName(), user.isActive(),
+                        admins.isAdmin(user.getEmail()), user.isTrap(), user.isShared(), pair.getT2(), pair.getT1(), user.getQuotaBytes() == null ? 0 : user.getQuotaBytes(),
                         user.getCreatedAt()));
     }
 
@@ -177,8 +232,6 @@ public class MailboxAdminController {
     }
 
     static String randomPassword() {
-        byte[] bytes = new byte[18];
-        new SecureRandom().nextBytes(bytes);
-        return Base64.getUrlEncoder().withoutPadding().encodeToString(bytes);
+        return MailDirectory.randomPassword();
     }
 }

backend/src/main/java/com/mailserver/controller/MailboxesController.java

@@ -0,0 +1,130 @@
+package com.mailserver.controller;
+
+import com.mailserver.domain.User;
+import com.mailserver.dto.LoginResponse;
+import com.mailserver.security.Actor;
+import com.mailserver.security.LoginGuard;
+import com.mailserver.service.MailboxAccess;
+import com.mailserver.service.UserService;
+import com.mailserver.util.JwtUtils;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Size;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.security.core.Authentication;
+import org.springframework.web.bind.annotation.DeleteMapping;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.ResponseStatus;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.server.ResponseStatusException;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.time.Duration;
+import java.util.Locale;
+
+/**
+ * The mailboxes of the logged-in user (left menu): own, shared ones it is a member of, attached ones.
+ * Always works for the LOGIN behind the session, also when a shared mailbox is open.
+ */
+@RestController
+@RequestMapping("/api/mailboxes")
+public class MailboxesController {
+
+    private static final Logger log = LoggerFactory.getLogger(MailboxesController.class);
+
+    public record AttachRequest(@NotBlank @Size(max = 254) String email, @NotBlank @Size(max = 200) String password) {
+    }
+
+    private final MailboxAccess access;
+    private final UserService users;
+    private final JwtUtils jwt;
+    private final LoginGuard guard;
+
+    public MailboxesController(MailboxAccess access, UserService users, JwtUtils jwt, LoginGuard guard) {
+        this.access = access;
+        this.users = users;
+        this.jwt = jwt;
+        this.guard = guard;
+    }
+
+    @GetMapping
+    public Flux<MailboxAccess.Entry> mine(Mono<Authentication> auth) {
+        return login(auth).flatMapMany(access::mailboxes);
+    }
+
+    /** A session of this mailbox for the login (switch in the left menu). */
+    @PostMapping("/{email}/session")
+    public Mono<LoginResponse> session(Mono<Authentication> auth, @PathVariable String email) {
+        return login(auth).flatMap(me -> mailbox(email).flatMap(target -> access.has(target.getId(), me.getId())
+                .flatMap(allowed -> {
+                    if (!allowed) {
+                        return Mono.error(new ResponseStatusException(HttpStatus.FORBIDDEN, "No access to this mailbox"));
+                    }
+                    LoginResponse response = new LoginResponse();
+                    boolean own = target.getId().equals(me.getId());
+                    response.setToken(own ? jwt.generateToken(me.getEmail()) : jwt.generateToken(target.getEmail(), me.getEmail()));
+                    response.setEmail(target.getEmail());
+                    return Mono.just(response);
+                })));
+    }
+
+    /** Adds another mailbox the user knows the password of. The password is checked like a login (LoginGuard). */
+    @PostMapping("/attach")
+    @ResponseStatus(HttpStatus.CREATED)
+    public Mono<MailboxAccess.Entry> attach(Mono<Authentication> auth, @RequestBody Mono<AttachRequest> body, ServerHttpRequest http) {
+        String ip = AuthenticationController.clientIp(http);
+        return login(auth).zipWith(body).flatMap(pair -> {
+            User me = pair.getT1();
+            String email = pair.getT2().email().trim().toLowerCase(Locale.ROOT);
+            Duration wait = guard.retryAfter(ip, email);
+            if (!wait.isZero()) {
+                return Mono.error(new ResponseStatusException(HttpStatus.TOO_MANY_REQUESTS,
+                        "Too many failed attempts, try again in " + LoginGuard.human(wait)));
+            }
+            return users.findOptional(email)
+                    .filter(target -> target.isActive() && !target.isShared() && users.checkPassword(target, pair.getT2().password()))
+                    .switchIfEmpty(Mono.defer(() -> {
+                        guard.failure(ip, email);
+                        log.warn("WEB {}: {} failed to attach {}", ip, me.getEmail(), email);
+                        return Mono.error(new ResponseStatusException(HttpStatus.BAD_REQUEST, "Wrong address or password"));
+                    }))
+                    .flatMap(target -> {
+                        if (target.getId().equals(me.getId())) {
+                            return Mono.error(new ResponseStatusException(HttpStatus.BAD_REQUEST, "This is your own mailbox"));
+                        }
+                        guard.success(ip, email);
+                        log.info("{} attached mailbox {}", me.getEmail(), email);
+                        return access.grant(target.getId(), me.getId(), MailboxAccess.ATTACHED)
+                                .then(access.unread(target.getId()))
+                                .map(n -> new MailboxAccess.Entry(target.getEmail(), target.getDisplayName(), MailboxAccess.ATTACHED, false, n));
+                    });
+        });
+    }
+
+    /** Removes the mailbox from the user's menu (attached or shared). */
+    @DeleteMapping("/{email}")
+    @ResponseStatus(HttpStatus.NO_CONTENT)
+    public Mono<Void> leave(Mono<Authentication> auth, @PathVariable String email) {
+        return login(auth).flatMap(me -> mailbox(email).flatMap(target -> access.revoke(target.getId(), me.getId())
+                .flatMap(done -> done ? Mono.<Void>empty()
+                        : Mono.error(new ResponseStatusException(HttpStatus.NOT_FOUND, "Not in your mailboxes")))));
+    }
+
+    private Mono<User> login(Mono<Authentication> auth) {
+        return auth.switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.UNAUTHORIZED)))
+                .flatMap(a -> users.findOptional(Actor.login(a)))
+                .switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.UNAUTHORIZED)));
+    }
+
+    private Mono<User> mailbox(String email) {
+        return users.findOptional(email)
+                .switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.NOT_FOUND, "No such mailbox")));
+    }
+}

backend/src/main/java/com/mailserver/controller/ServiceController.java

@@ -0,0 +1,183 @@
+package com.mailserver.controller;
+
+import com.mailserver.domain.User;
+import com.mailserver.service.MailDirectory;
+import com.mailserver.service.MailLists;
+import com.mailserver.service.MailboxAccess;
+import com.mailserver.service.UserService;
+import jakarta.validation.constraints.Size;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.DeleteMapping;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.PutMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestHeader;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.server.ResponseStatusException;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.util.List;
+
+/**
+ * Service API for Jambotron (staff mailboxes): token {@code SERVICE_TOKEN} in {@code Authorization: Bearer …}.
+ * Without the token configured the API is off (404). Accounts: create (password returned ONCE), switch on/off,
+ * new password; lists: the exact settings and members, Jambotron is the source of truth for the lists it keeps.
+ */
+@RestController
+@RequestMapping("/api/service")
+public class ServiceController {
+
+    private static final Logger log = LoggerFactory.getLogger(ServiceController.class);
+
+    /** @param displayName null — unchanged (new account: the name before @) */
+    public record AccountRequest(@Size(max = 100) String displayName, Boolean active) {
+    }
+
+    public record AccountView(String email, String displayName, boolean active, List<String> lists) {
+    }
+
+    /** @param password generated, only when the account was just created or got a new password */
+    public record AccountResult(AccountView account, String password) {
+    }
+
+    public record ListRequest(@Size(max = 50) String folder, @Size(max = 255) String description, boolean openToOutside,
+                              List<String> members) {
+    }
+
+    private final byte[] token;
+    private final UserService users;
+    private final MailLists lists;
+    private final MailDirectory directory;
+    private final MailboxAccess access;
+
+    public ServiceController(@Value("${mailserver.service-token:}") String token, UserService users, MailLists lists,
+                             MailDirectory directory, MailboxAccess access) {
+        this.access = access;
+        this.token = token.isBlank() ? null : token.trim().getBytes(StandardCharsets.UTF_8);
+        this.users = users;
+        this.lists = lists;
+        this.directory = directory;
+    }
+
+    @GetMapping("/accounts/{email}")
+    public Mono<AccountView> account(@RequestHeader(value = "Authorization", required = false) String auth,
+                                     @PathVariable String email) {
+        check(auth);
+        return users.findOptional(email)
+                .switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.NOT_FOUND, "No such mailbox")))
+                .flatMap(this::view);
+    }
+
+    /** Creates the account (201 + password once) or updates name / on-off (200). Switched off → out of every list. */
+    @PutMapping("/accounts/{email}")
+    public Mono<ResponseEntity<AccountResult>> saveAccount(@RequestHeader(value = "Authorization", required = false) String auth,
+                                                           @PathVariable String email, @RequestBody Mono<AccountRequest> body) {
+        check(auth);
+        String address = directory.address(email);
+        return body.defaultIfEmpty(new AccountRequest(null, null)).flatMap(request -> users.findOptional(address)
+                .flatMap(user -> update(user, request).flatMap(this::view)
+                        .map(view -> ResponseEntity.ok(new AccountResult(view, null))))
+                .switchIfEmpty(Mono.defer(() -> {
+                    String password = MailDirectory.randomPassword();
+                    return directory.createMailbox(address, request.displayName(), password)
+                            .flatMap(user -> Boolean.FALSE.equals(request.active()) ? update(user, request) : Mono.just(user))
+                            .doOnNext(user -> log.info("Mailbox {} created by Jambotron", user.getEmail()))
+                            .flatMap(this::view)
+                            .map(view -> ResponseEntity.status(HttpStatus.CREATED).body(new AccountResult(view, password)));
+                })));
+    }
+
+    /** New generated password, returned once (Jambotron profile → «new mail password»). */
+    @PostMapping("/accounts/{email}/password")
+    public Mono<AccountResult> password(@RequestHeader(value = "Authorization", required = false) String auth,
+                                        @PathVariable String email) {
+        check(auth);
+        String password = MailDirectory.randomPassword();
+        return users.findOptional(email)
+                .switchIfEmpty(Mono.error(new ResponseStatusException(HttpStatus.NOT_FOUND, "No such mailbox")))
+                .flatMap(user -> users.setPassword(user, password))
+                .doOnNext(user -> log.info("Password of {} set by Jambotron", user.getEmail()))
+                .flatMap(this::view)
+                .map(view -> new AccountResult(view, password));
+    }
+
+    @GetMapping("/lists")
+    public Flux<MailLists.MailList> lists(@RequestHeader(value = "Authorization", required = false) String auth) {
+        check(auth);
+        return lists.all();
+    }
+
+    @PutMapping("/lists/{address}")
+    public Mono<MailLists.MailList> saveList(@RequestHeader(value = "Authorization", required = false) String auth,
+                                             @PathVariable String address, @RequestBody Mono<ListRequest> body) {
+        check(auth);
+        return body.flatMap(request -> directory.saveList(address, request.folder(), request.description(),
+                        request.openToOutside(), request.members()))
+                .doOnNext(list -> log.info("List {} saved by Jambotron: {}", list.address(), list.members()));
+    }
+
+    @DeleteMapping("/lists/{address}")
+    public Mono<ResponseEntity<Void>> deleteList(@RequestHeader(value = "Authorization", required = false) String auth,
+                                                 @PathVariable String address) {
+        check(auth);
+        return lists.delete(address).map(deleted -> deleted
+                ? ResponseEntity.noContent().<Void>build() : ResponseEntity.notFound().<Void>build());
+    }
+
+    public record SharedRequest(@Size(max = 100) String displayName, List<String> members) {
+    }
+
+    public record SharedView(String email, String displayName, List<String> members) {
+    }
+
+    /** Shared mailbox (support@, billing@): created when missing, exactly these members. */
+    @PutMapping("/shared/{address}")
+    public Mono<SharedView> saveShared(@RequestHeader(value = "Authorization", required = false) String auth,
+                                       @PathVariable String address, @RequestBody Mono<SharedRequest> body) {
+        check(auth);
+        return body.flatMap(request -> directory.saveShared(address, request.displayName(), request.members()))
+                .flatMap(user -> access.members(user.getId()).collectList()
+                        .map(members -> new SharedView(user.getEmail(), user.getDisplayName(), members)))
+                .doOnNext(view -> log.info("Shared mailbox {} saved by Jambotron: {}", view.email(), view.members()));
+    }
+
+    private Mono<User> update(User user, AccountRequest request) {
+        Mono<User> named = request.displayName() == null || request.displayName().isBlank() ? Mono.just(user)
+                : users.updateDisplayName(user, request.displayName());
+        if (request.active() == null || request.active() == user.isActive()) {
+            return named;
+        }
+        boolean on = request.active();
+        return named.flatMap(u -> users.setActive(u, on))
+                .flatMap(u -> on ? Mono.just(u) : lists.removeEverywhere(u.getId())
+                        .then(access.removeEverywhere(u.getId())).thenReturn(u))
+                .doOnNext(u -> log.info("Mailbox {} {} by Jambotron", u.getEmail(), on ? "switched on" : "switched off"));
+    }
+
+    private Mono<AccountView> view(User user) {
+        return lists.listsOf(user.getId()).collectList()
+                .map(in -> new AccountView(user.getEmail(), user.getDisplayName(), user.isActive(), in));
+    }
+
+    /** 404 when the API is off, 401 for a wrong token (constant-time compare). */
+    private void check(String auth) {
+        if (token == null) {
+            throw new ResponseStatusException(HttpStatus.NOT_FOUND);
+        }
+        byte[] given = auth != null && auth.startsWith("Bearer ")
+                ? auth.substring(7).trim().getBytes(StandardCharsets.UTF_8) : new byte[0];
+        if (!MessageDigest.isEqual(token, given)) {
+            throw new ResponseStatusException(HttpStatus.UNAUTHORIZED);
+        }
+    }
+}

backend/src/main/java/com/mailserver/domain/Message.java

@@ -54,6 +54,13 @@ public class Message {
     @Column("message_id")
     private String messageId;
 
+    /** Who answered it from the web client (V7) — the login, also for a shared mailbox. */
+    @Column("answered_by")
+    private String answeredBy;
+
+    public String getAnsweredBy() { return answeredBy; }
+    public void setAnsweredBy(String answeredBy) { this.answeredBy = answeredBy; }
+
     public Long getId() { return id; }
     public void setId(Long id) { this.id = id; }
 

backend/src/main/java/com/mailserver/domain/User.java

@@ -30,6 +30,14 @@ public class User {
     @Column("is_active")
     private boolean isActive = true;
 
+    /** Trap: what this mailbox sends is stored in its own INBOX, never delivered (V5). */
+    @Column("is_trap")
+    private boolean isTrap = false;
+
+    /** Shared mailbox (V7): no login of its own, members open it. */
+    @Column("is_shared")
+    private boolean isShared = false;
+
     @Column("created_at")
     private Instant createdAt;
 
@@ -54,6 +62,12 @@ public class User {
     public boolean isActive() { return isActive; }
     public void setActive(boolean active) { isActive = active; }
 
+    public boolean isTrap() { return isTrap; }
+    public void setTrap(boolean trap) { isTrap = trap; }
+
+    public boolean isShared() { return isShared; }
+    public void setShared(boolean shared) { isShared = shared; }
+
     public Instant getCreatedAt() { return createdAt; }
     public void setCreatedAt(Instant createdAt) { this.createdAt = createdAt; }
 }

backend/src/main/java/com/mailserver/dto/MessageResponse.java

@@ -20,6 +20,11 @@ public class MessageResponse {
     private Long folderId;
     private boolean hasAttachments;
     private int attachmentCount;
+    /** login that answered it from the web client, or null */
+    private String answeredBy;
+
+    public String getAnsweredBy() { return answeredBy; }
+    public void setAnsweredBy(String answeredBy) { this.answeredBy = answeredBy; }
 
     public Long getId() { return id; }
     public void setId(Long id) { this.id = id; }

backend/src/main/java/com/mailserver/dto/SendRequest.java

@@ -26,6 +26,12 @@ public class SendRequest {
 
     private Long draftId;
 
+    /** The message this one answers (web client «Reply»): marked answered, by whom. */
+    private Long replyToId;
+
+    public Long getReplyToId() { return replyToId; }
+    public void setReplyToId(Long replyToId) { this.replyToId = replyToId; }
+
     public String getTo() { return to; }
     public void setTo(String to) { this.to = to; }
 

backend/src/main/java/com/mailserver/imap/DbImapStore.java

@@ -8,6 +8,7 @@ import com.mailserver.repository.MessageRepository;
 import com.mailserver.repository.UserRepository;
 import com.mailserver.service.LocalDelivery;
 import com.mailserver.service.MailService;
+import com.mailserver.service.MailboxAccess;
 import com.mailserver.service.MessageSources;
 import com.mailserver.service.UserService;
 import jakarta.mail.Session;
@@ -45,10 +46,12 @@ public class DbImapStore implements ImapStore {
     private final AttachmentRepository attachments;
     private final MessageSources sources;
     private final String hostname;
+    private final MailboxAccess access;
 
     public DbImapStore(DatabaseClient db, UserRepository users, UserService userService, MailService mailService,
                        MessageRepository messages, AttachmentRepository attachments, MessageSources sources,
-                       String hostname) {
+                       String hostname, MailboxAccess access) {
+        this.access = access;
         this.db = db;
         this.users = users;
         this.userService = userService;
@@ -61,11 +64,9 @@ public class DbImapStore implements ImapStore {
 
     @Override
     public Account authenticate(String username, String password) {
-        User user = users.findByEmail(username.trim().toLowerCase(Locale.ROOT)).block();
-        if (user == null || !user.isActive() || !userService.checkPassword(user, password)) {
-            return null;
-        }
-        return new Account(user.getId(), user.getEmail());
+        // login or mailbox*login (shared / attached mailbox in a mail program)
+        User user = access.login(username, password);
+        return user == null ? null : new Account(user.getId(), user.getEmail());
     }
 
     @Override

backend/src/main/java/com/mailserver/security/Actor.java

@@ -0,0 +1,23 @@
+package com.mailserver.security;
+
+import org.springframework.security.core.Authentication;
+
+/**
+ * Who is acting: the mailbox the session belongs to ({@link Authentication#getName()}) and the login behind it —
+ * the same for an own session, another one when a member opened a shared mailbox or an administrator opened one.
+ */
+public final class Actor {
+
+    private Actor() {
+    }
+
+    /** The login behind the session. */
+    public static String login(Authentication auth) {
+        return auth.getDetails() instanceof String by && !by.isBlank() ? by : auth.getName();
+    }
+
+    /** The session is another login's view of this mailbox: no password / profile changes from it. */
+    public static boolean opened(Authentication auth) {
+        return !login(auth).equalsIgnoreCase(auth.getName());
+    }
+}

backend/src/main/java/com/mailserver/security/JwtAuthenticationFilter.java

@@ -43,6 +43,8 @@ public class JwtAuthenticationFilter implements WebFilter {
                 UserDetails userDetails = new User(email, "", Collections.emptyList());
                 UsernamePasswordAuthenticationToken authentication =
                         new UsernamePasswordAuthenticationToken(userDetails, null, Collections.emptyList());
+                // the login that opened this mailbox (shared / attached / administrator's OPEN); see Actor
+                authentication.setDetails(jwtUtils.getByFromToken(token));
 
                 return chain.filter(exchange)
                         .contextWrite(ReactiveSecurityContextHolder.withAuthentication(authentication));

backend/src/main/java/com/mailserver/service/LocalDelivery.java

@@ -54,6 +54,12 @@ public class LocalDelivery implements DeliveryWorker.BounceSender {
     /** Blocking: call from a worker thread. */
     public void deliver(byte[] raw, String mailbox, String remoteIp, String envelopeFrom, boolean trusted)
             throws MessagingException, IOException {
+        deliver(raw, mailbox, null, remoteIp, envelopeFrom, trusted);
+    }
+
+    /** @param folder own folder of the mailbox ("+tag", mailing list), created when missing; null — INBOX */
+    public void deliver(byte[] raw, String mailbox, String folder, String remoteIp, String envelopeFrom, boolean trusted)
+            throws MessagingException, IOException {
         MimeMessage mime = new MimeMessage(Session.getInstance(new Properties()), new ByteArrayInputStream(raw));
 
         String senderEmail = envelopeFrom;
@@ -80,7 +86,7 @@ public class LocalDelivery implements DeliveryWorker.BounceSender {
         com.mailserver.domain.Message stored =
                 mailService.receiveMessage(senderEmail, senderName, mailbox, subject, body.text(), body.html(), spam,
                         addresses(mime, jakarta.mail.Message.RecipientType.TO),
-                        addresses(mime, jakarta.mail.Message.RecipientType.CC)).block();
+                        addresses(mime, jakarta.mail.Message.RecipientType.CC), folder).block();
         if (stored != null) {
             for (FilePart file : attachments(mime)) {
                 mailService.storeIncomingAttachment(stored.getId(), file.name(), file.contentType(), file.bytes());

backend/src/main/java/com/mailserver/service/MailDirectory.java

@@ -0,0 +1,132 @@
+package com.mailserver.service;
+
+import com.mailserver.config.MailDomains;
+import com.mailserver.domain.User;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Service;
+import org.springframework.web.server.ResponseStatusException;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.security.SecureRandom;
+import java.util.ArrayList;
+import java.util.Base64;
+import java.util.List;
+import java.util.Locale;
+import java.util.regex.Pattern;
+
+/**
+ * Mailboxes and mailing lists share one address space: one rule for both, used by Settings (administrators)
+ * and by the service API (Jambotron). Names never contain "+" — the part after it is a folder label.
+ */
+@Service
+public class MailDirectory {
+
+    private static final Pattern LOCAL_PART = Pattern.compile("[a-z0-9](?:[a-z0-9._-]{0,62}[a-z0-9])?");
+    private static final Pattern FOLDER = Pattern.compile("[A-Za-z0-9][A-Za-z0-9._-]{0,49}");
+    public static final int MIN_PASSWORD = 8;
+
+    private final UserService users;
+    private final MailLists lists;
+    private final MailDomains domains;
+    private final MailboxAccess access;
+
+    public MailDirectory(UserService users, MailLists lists, MailDomains domains, MailboxAccess access) {
+        this.access = access;
+        this.users = users;
+        this.lists = lists;
+        this.domains = domains;
+    }
+
+    /** Lower-case address of our domain with an allowed name, or 400. */
+    public String address(String raw) {
+        String email = raw == null ? "" : raw.trim().toLowerCase(Locale.ROOT);
+        int at = email.lastIndexOf('@');
+        if (at <= 0 || !LOCAL_PART.matcher(email.substring(0, at)).matches()) {
+            throw bad("Not a mailbox address: " + email + " (letters, digits, . _ - ; no +)");
+        }
+        if (!domains.isLocal(email)) {
+            throw bad("Only in " + String.join(", ", domains.domains().stream().sorted().toList()));
+        }
+        return email;
+    }
+
+    /** New mailbox; the address must not be taken by a mailbox or a list. 409 when taken. */
+    public Mono<User> createMailbox(String rawEmail, String displayName, String password) {
+        String email = address(rawEmail);
+        if (password == null || password.length() < MIN_PASSWORD) {
+            return Mono.error(bad("Password: at least " + MIN_PASSWORD + " characters"));
+        }
+        return lists.exists(email).flatMap(isList -> isList
+                ? Mono.<User>error(new ResponseStatusException(HttpStatus.CONFLICT, "This address is a mailing list"))
+                : users.register(email, password, displayName)
+                        .onErrorMap(IllegalArgumentException.class,
+                                e -> new ResponseStatusException(HttpStatus.CONFLICT, "This mailbox already exists")));
+    }
+
+    /**
+     * Creates or replaces a list. Members: mailboxes of this server (addresses); unknown ones → 400 naming them.
+     */
+    public Mono<MailLists.MailList> saveList(String rawAddress, String rawFolder, String description,
+                                             boolean openToOutside, List<String> members) {
+        String address = address(rawAddress);
+        String folder = rawFolder == null || rawFolder.isBlank() ? null : rawFolder.trim();
+        if (folder != null && (!FOLDER.matcher(folder).matches()
+                || MailService.SYSTEM_FOLDERS.stream().anyMatch(folder::equalsIgnoreCase))) {
+            return Mono.error(bad("Folder: letters, digits, . _ - (up to 50), not a system folder; empty — INBOX"));
+        }
+        String about = description == null || description.isBlank() ? null : description.trim();
+        if (about != null && about.length() > 255) {
+            return Mono.error(bad("Description: up to 255 characters"));
+        }
+        List<String> wanted = members == null ? List.of()
+                : members.stream().map(m -> m.trim().toLowerCase(Locale.ROOT)).filter(m -> !m.isEmpty()).distinct().toList();
+        return users.findOptional(address).hasElement().flatMap(isMailbox -> {
+            if (isMailbox) {
+                return Mono.error(new ResponseStatusException(HttpStatus.CONFLICT, "This address is a mailbox"));
+            }
+            List<String> unknown = new ArrayList<>();
+            return Flux.fromIterable(wanted)
+                    .concatMap(member -> users.findOptional(member)
+                            .map(User::getId)
+                            .switchIfEmpty(Mono.fromRunnable(() -> unknown.add(member))))
+                    .collectList()
+                    .flatMap(ids -> unknown.isEmpty()
+                            ? lists.save(address, folder, about, openToOutside, ids)
+                            : Mono.error(bad("No such mailbox: " + String.join(", ", unknown))));
+        });
+    }
+
+    /** Exactly these members (mailboxes of this server) for the mailbox; unknown ones → 400 naming them. */
+    public Mono<Void> setMembers(User mailbox, List<String> members) {
+        List<String> wanted = members == null ? List.of()
+                : members.stream().map(m -> m.trim().toLowerCase(Locale.ROOT)).filter(m -> !m.isEmpty()).distinct().toList();
+        List<String> unknown = new ArrayList<>();
+        return Flux.fromIterable(wanted)
+                .concatMap(member -> users.findOptional(member).map(User::getId)
+                        .switchIfEmpty(Mono.fromRunnable(() -> unknown.add(member))))
+                .collectList()
+                .flatMap(ids -> unknown.isEmpty() ? access.setMembers(mailbox.getId(), ids)
+                        : Mono.error(bad("No such mailbox: " + String.join(", ", unknown))));
+    }
+
+    /** Shared mailbox: created when missing (no login of its own), then exactly these members. */
+    public Mono<User> saveShared(String rawAddress, String displayName, List<String> members) {
+        String address = address(rawAddress);
+        return users.findOptional(address)
+                .switchIfEmpty(Mono.defer(() -> createMailbox(address, displayName, randomPassword())))
+                .flatMap(user -> user.isShared() ? Mono.just(user) : users.setShared(user, true))
+                .flatMap(user -> displayName == null || displayName.isBlank() ? Mono.just(user) : users.updateDisplayName(user, displayName))
+                .flatMap(user -> setMembers(user, members).thenReturn(user));
+    }
+
+    public static String randomPassword() {
+        byte[] bytes = new byte[18];
+        new SecureRandom().nextBytes(bytes);
+        return Base64.getUrlEncoder().withoutPadding().encodeToString(bytes);
+    }
+
+    public static ResponseStatusException bad(String message) {
+        return new ResponseStatusException(HttpStatus.BAD_REQUEST, message);
+    }
+}

backend/src/main/java/com/mailserver/service/MailLists.java

@@ -0,0 +1,101 @@
+package com.mailserver.service;
+
+import org.springframework.r2dbc.core.DatabaseClient;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.Locale;
+
+/**
+ * Mailing lists (V6): {@code alerts-prod@} → every member gets their own copy in the list's folder.
+ * Kept by the administrators (Settings → LISTS) and by Jambotron through the service API.
+ */
+@Service
+public class MailLists {
+
+    /** @param folder where members get the copy; null — INBOX */
+    public record MailList(Long id, String address, String folder, String description, boolean openToOutside,
+                           List<String> members) {
+    }
+
+    private final DatabaseClient db;
+
+    public MailLists(DatabaseClient db) {
+        this.db = db;
+    }
+
+    public Mono<MailList> find(String address) {
+        return db.sql("SELECT id, address, folder, description, open_to_outside FROM mail_lists WHERE address = :a")
+                .bind("a", address.toLowerCase(Locale.ROOT))
+                .map((row, meta) -> new MailList(row.get("id", Long.class), row.get("address", String.class),
+                        row.get("folder", String.class), row.get("description", String.class),
+                        Boolean.TRUE.equals(row.get("open_to_outside", Boolean.class)), List.of()))
+                .one()
+                .flatMap(this::withMembers);
+    }
+
+    public Mono<Boolean> exists(String address) {
+        return db.sql("SELECT 1 FROM mail_lists WHERE address = :a").bind("a", address.toLowerCase(Locale.ROOT))
+                .map((row, meta) -> true).one().defaultIfEmpty(false);
+    }
+
+    public Flux<MailList> all() {
+        return db.sql("SELECT id, address, folder, description, open_to_outside FROM mail_lists ORDER BY address")
+                .map((row, meta) -> new MailList(row.get("id", Long.class), row.get("address", String.class),
+                        row.get("folder", String.class), row.get("description", String.class),
+                        Boolean.TRUE.equals(row.get("open_to_outside", Boolean.class)), List.of()))
+                .all()
+                .concatMap(this::withMembers);
+    }
+
+    /** Lists this mailbox is a member of (shown to the mailbox owner). */
+    public Flux<String> listsOf(Long userId) {
+        return db.sql("SELECT l.address FROM mail_lists l JOIN mail_list_members m ON m.list_id = l.id "
+                        + "WHERE m.user_id = :u ORDER BY l.address")
+                .bind("u", userId).map((row, meta) -> row.get("address", String.class)).all();
+    }
+
+    /**
+     * Creates or replaces the list: settings and the exact member set. Members are mailbox ids (checked by the caller).
+     */
+    @Transactional
+    public Mono<MailList> save(String address, String folder, String description, boolean openToOutside,
+                               Collection<Long> memberIds) {
+        String a = address.toLowerCase(Locale.ROOT);
+        var insert = db.sql("INSERT INTO mail_lists (address, folder, description, open_to_outside) "
+                        + "VALUES (:a, :f, :d, :o) ON CONFLICT (address) DO UPDATE "
+                        + "SET folder = EXCLUDED.folder, description = EXCLUDED.description, "
+                        + "open_to_outside = EXCLUDED.open_to_outside RETURNING id")
+                .bind("a", a).bind("o", openToOutside);
+        insert = folder == null ? insert.bindNull("f", String.class) : insert.bind("f", folder);
+        insert = description == null ? insert.bindNull("d", String.class) : insert.bind("d", description);
+        return insert.map((row, meta) -> row.get("id", Long.class)).one()
+                .flatMap(id -> db.sql("DELETE FROM mail_list_members WHERE list_id = :l").bind("l", id).then()
+                        .thenMany(Flux.fromIterable(memberIds).distinct()
+                                .concatMap(member -> db.sql("INSERT INTO mail_list_members (list_id, user_id) VALUES (:l, :u)")
+                                        .bind("l", id).bind("u", member).then()))
+                        .then(find(a)));
+    }
+
+    public Mono<Boolean> delete(String address) {
+        return db.sql("DELETE FROM mail_lists WHERE address = :a").bind("a", address.toLowerCase(Locale.ROOT))
+                .fetch().rowsUpdated().map(n -> n > 0);
+    }
+
+    /** Takes the mailbox out of every list (mailbox switched off / role removed in Jambotron). */
+    public Mono<Long> removeEverywhere(Long userId) {
+        return db.sql("DELETE FROM mail_list_members WHERE user_id = :u").bind("u", userId).fetch().rowsUpdated();
+    }
+
+    private Mono<MailList> withMembers(MailList list) {
+        return db.sql("SELECT u.email FROM mail_list_members m JOIN users u ON u.id = m.user_id "
+                        + "WHERE m.list_id = :l ORDER BY u.email")
+                .bind("l", list.id()).map((row, meta) -> row.get("email", String.class)).all().collectList()
+                .map(members -> new MailList(list.id(), list.address(), list.folder(), list.description(),
+                        list.openToOutside(), members));
+    }
+}

backend/src/main/java/com/mailserver/service/MailService.java

@@ -162,6 +162,34 @@ public class MailService {
                 .switchIfEmpty(Mono.error(badRequest("System folders cannot be renamed or deleted")));
     }
 
+    private static final java.util.regex.Pattern DELIVERY_FOLDER = java.util.regex.Pattern.compile("[A-Za-z0-9][A-Za-z0-9._-]{0,49}");
+
+    /**
+     * A "+tag" / list folder that may be used as a folder name, or null (→ INBOX). A sender never puts mail into
+     * a system folder (Spam, Trash, Sent …) this way.
+     */
+    static String deliveryFolderName(String raw) {
+        if (raw == null || !DELIVERY_FOLDER.matcher(raw).matches() || SYSTEM_FOLDERS.stream().anyMatch(raw::equalsIgnoreCase)) {
+            return null;
+        }
+        return raw;
+    }
+
+    /** The folder with this name (any case), created as an own folder when missing; two at once — one wins. */
+    private Mono<Folder> deliveryFolder(Long userId, String name) {
+        Mono<Folder> existing = folderRepository.findByUserId(userId)
+                .filter(folder -> folder.getName().equalsIgnoreCase(name))
+                .next();
+        return existing.switchIfEmpty(Mono.defer(() -> {
+            Folder folder = new Folder();
+            folder.setUserId(userId);
+            folder.setName(name);
+            folder.setCreatedAt(Instant.now());
+            return folderRepository.save(folder)
+                    .onErrorResume(org.springframework.dao.DataIntegrityViolationException.class, e -> existing);
+        }));
+    }
+
     private Mono<Folder> systemFolder(Long userId, String name) {
         return folderRepository.findByUserIdAndName(userId, name)
                 .switchIfEmpty(Mono.error(new IllegalStateException(name + " folder not found")));
@@ -253,12 +281,25 @@ public class MailService {
     public Mono<Message> receiveMessage(String senderEmail, String senderName, String recipientEmail,
                                String subject, String body, boolean isHtml, boolean externalSpamFlag,
                                String toHeader, String ccHeader) {
+        return receiveMessage(senderEmail, senderName, recipientEmail, subject, body, isHtml, externalSpamFlag,
+                toHeader, ccHeader, null);
+    }
+
+    /**
+     * @param folder own folder for the message ("+tag" of the address, folder of a mailing list), created when
+     *               missing; null or not a valid folder name — INBOX. Spam still goes to Spam.
+     */
+    public Mono<Message> receiveMessage(String senderEmail, String senderName, String recipientEmail,
+                               String subject, String body, boolean isHtml, boolean externalSpamFlag,
+                               String toHeader, String ccHeader, String targetFolder) {
         return userRepository.findByEmail(recipientEmail)
                 .switchIfEmpty(Mono.error(new IllegalArgumentException("Recipient not found: " + recipientEmail)))
                 .flatMap(recipient -> spamFilterService.isBlacklisted(recipient.getId(), senderEmail)
                         .flatMap(blacklisted -> {
                             boolean isSpam = blacklisted || externalSpamFlag;
-                            return systemFolder(recipient.getId(), isSpam ? "Spam" : "INBOX")
+                            String own = isSpam ? null : deliveryFolderName(targetFolder);
+                            return (own == null ? systemFolder(recipient.getId(), isSpam ? "Spam" : "INBOX")
+                                    : deliveryFolder(recipient.getId(), own))
                                     .flatMap(folder -> {
                                         Message message = new Message();
                                         message.setFolderId(folder.getId());
@@ -439,6 +480,7 @@ public class MailService {
         resp.setMessageSize(message.getMessageSize());
         resp.setReceivedAt(message.getReceivedAt());
         resp.setFolderId(message.getFolderId());
+        resp.setAnsweredBy(message.getAnsweredBy());
         return resp;
     }
 

backend/src/main/java/com/mailserver/service/MailboxAccess.java

@@ -0,0 +1,129 @@
+package com.mailserver.service;
+
+import com.mailserver.domain.User;
+import com.mailserver.repository.UserRepository;
+import org.springframework.r2dbc.core.DatabaseClient;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.util.Collection;
+import java.util.Locale;
+
+/**
+ * Several mailboxes for one login (V7): own, shared ones it is a MEMBER of, ATTACHED ones (by their password).
+ * One rule for the web client, SMTP and IMAP; in mail programs another mailbox is
+ * {@code mailbox*login} with the login's password (the Dovecot "master user" form).
+ */
+@Service
+public class MailboxAccess {
+
+    public static final String MEMBER = "MEMBER";
+    public static final String ATTACHED = "ATTACHED";
+
+    /** @param kind OWN, MEMBER or ATTACHED; unread — INBOX and own folders (not Spam/Trash/Sent/Drafts) */
+    public record Entry(String email, String displayName, String kind, boolean shared, long unread) {
+    }
+
+    private final DatabaseClient db;
+    private final UserRepository users;
+    private final UserService userService;
+
+    public MailboxAccess(DatabaseClient db, UserRepository users, UserService userService) {
+        this.db = db;
+        this.users = users;
+        this.userService = userService;
+    }
+
+    /**
+     * Login for SMTP / IMAP: {@code login} or {@code mailbox*login} + the login's password → the mailbox the
+     * session works with, or null. A shared mailbox never logs in by itself.
+     */
+    public User login(String username, String password) {
+        String name = username.trim().toLowerCase(Locale.ROOT);
+        int star = name.indexOf('*');
+        String mailbox = star < 0 ? name : name.substring(0, star);
+        String login = star < 0 ? name : name.substring(star + 1);
+        User user = users.findByEmail(login).block();
+        if (user == null || !user.isActive() || user.isShared() || !userService.checkPassword(user, password)) {
+            return null;
+        }
+        if (mailbox.equals(login)) {
+            return user;
+        }
+        User target = users.findByEmail(mailbox).block();
+        return target != null && target.isActive() && Boolean.TRUE.equals(has(target.getId(), user.getId()).block())
+                ? target : null;
+    }
+
+    /** The login may open this mailbox (own or by access). */
+    public Mono<Boolean> has(Long mailboxId, Long userId) {
+        if (mailboxId.equals(userId)) {
+            return Mono.just(true);
+        }
+        return db.sql("SELECT 1 FROM mailbox_access WHERE mailbox_id = :m AND user_id = :u")
+                .bind("m", mailboxId).bind("u", userId).map((row, meta) -> true).one().defaultIfEmpty(false);
+    }
+
+    /** Own mailbox first, then the others by address. */
+    public Flux<Entry> mailboxes(User login) {
+        Mono<Entry> own = unread(login.getId()).map(n -> new Entry(login.getEmail(), login.getDisplayName(), "OWN", false, n));
+        Flux<Entry> others = db.sql("SELECT u.id, u.email, u.display_name, u.is_shared, a.kind FROM mailbox_access a "
+                        + "JOIN users u ON u.id = a.mailbox_id WHERE a.user_id = :u AND u.is_active ORDER BY u.email")
+                .bind("u", login.getId())
+                .map((row, meta) -> new Object[]{row.get("id", Long.class), row.get("email", String.class),
+                        row.get("display_name", String.class), Boolean.TRUE.equals(row.get("is_shared", Boolean.class)),
+                        row.get("kind", String.class)})
+                .all()
+                .concatMap(r -> unread((Long) r[0]).map(n -> new Entry((String) r[1], (String) r[2], (String) r[4], (Boolean) r[3], n)));
+        return own.flux().concatWith(others);
+    }
+
+    public Mono<Long> unread(Long mailboxId) {
+        return db.sql("SELECT COUNT(*) AS n FROM messages m JOIN folders f ON f.id = m.folder_id "
+                        + "WHERE f.user_id = :u AND NOT m.is_read AND NOT m.is_deleted AND (NOT f.is_system OR f.name = 'INBOX')")
+                .bind("u", mailboxId).map((row, meta) -> row.get("n", Long.class)).one().defaultIfEmpty(0L);
+    }
+
+    public Mono<Void> grant(Long mailboxId, Long userId, String kind) {
+        return db.sql("INSERT INTO mailbox_access (mailbox_id, user_id, kind) VALUES (:m, :u, :k) "
+                        + "ON CONFLICT (mailbox_id, user_id) DO NOTHING")
+                .bind("m", mailboxId).bind("u", userId).bind("k", kind).then();
+    }
+
+    public Mono<Boolean> revoke(Long mailboxId, Long userId) {
+        return db.sql("DELETE FROM mailbox_access WHERE mailbox_id = :m AND user_id = :u")
+                .bind("m", mailboxId).bind("u", userId).fetch().rowsUpdated().map(n -> n > 0);
+    }
+
+    /** Exactly these MEMBERs (ATTACHED ones stay — they know the password). */
+    @Transactional
+    public Mono<Void> setMembers(Long mailboxId, Collection<Long> memberIds) {
+        return db.sql("DELETE FROM mailbox_access WHERE mailbox_id = :m AND kind = :k").bind("m", mailboxId).bind("k", MEMBER).then()
+                .thenMany(Flux.fromIterable(memberIds).distinct().filter(id -> !id.equals(mailboxId))
+                        .concatMap(id -> db.sql("INSERT INTO mailbox_access (mailbox_id, user_id, kind) VALUES (:m, :u, :k) "
+                                        + "ON CONFLICT (mailbox_id, user_id) DO UPDATE SET kind = EXCLUDED.kind")
+                                .bind("m", mailboxId).bind("u", id).bind("k", MEMBER).then()))
+                .then();
+    }
+
+    public Flux<String> members(Long mailboxId) {
+        return db.sql("SELECT u.email FROM mailbox_access a JOIN users u ON u.id = a.user_id "
+                        + "WHERE a.mailbox_id = :m AND a.kind = :k ORDER BY u.email")
+                .bind("m", mailboxId).bind("k", MEMBER).map((row, meta) -> row.get("email", String.class)).all();
+    }
+
+    /** The login loses every MEMBER access (role removed in Jambotron); ATTACHED stays with the mailbox owner's say. */
+    public Mono<Long> removeEverywhere(Long userId) {
+        return db.sql("DELETE FROM mailbox_access WHERE user_id = :u AND kind = :k").bind("u", userId).bind("k", MEMBER)
+                .fetch().rowsUpdated();
+    }
+
+    /** Reply from the web client: the original is answered, and by whom. */
+    public Mono<Void> markAnswered(Long messageId, Long mailboxId, String by) {
+        return db.sql("UPDATE messages SET is_answered = TRUE, answered_by = :b WHERE id = :id "
+                        + "AND folder_id IN (SELECT id FROM folders WHERE user_id = :u)")
+                .bind("b", by).bind("id", messageId).bind("u", mailboxId).then();
+    }
+}

backend/src/main/java/com/mailserver/service/SubmissionService.java

@@ -50,9 +50,11 @@ public class SubmissionService {
     private final MailService mailService;
     private final MailRouter router;
     private final String hostname;
+    private final MailboxAccess access;
 
     public SubmissionService(UserRepository users, MailService mailService, MailRouter router,
-                             @Value("${mailserver.smtp.hostname:localhost}") String hostname) {
+                             @Value("${mailserver.smtp.hostname:localhost}") String hostname, MailboxAccess access) {
+        this.access = access;
         this.users = users;
         this.mailService = mailService;
         this.router = router;
@@ -60,6 +62,11 @@ public class SubmissionService {
     }
 
     public Mono<MessageResponse> send(String fromEmail, SendRequest request) {
+        return send(fromEmail, fromEmail, request);
+    }
+
+    /** @param login who sends (the member for a shared mailbox) — recorded as «answered by» on the original */
+    public Mono<MessageResponse> send(String fromEmail, String login, SendRequest request) {
         List<String> to = addresses(request.getTo());
         List<String> cc = addresses(request.getCc());
         cc.removeAll(to);
@@ -78,7 +85,9 @@ public class SubmissionService {
                                 .subscribeOn(Schedulers.boundedElastic()))
                         .flatMap(messageId -> mailService.saveSent(user, String.join(", ", to), String.join(", ", cc),
                                 request.getSubject(), request.getBody(), request.isHtml(), messageId))
-                        .flatMap(sent -> (draftId == null ? Mono.<Void>empty() : mailService.finishDraft(draftId, sent.getId()))
+                        .flatMap(sent -> (request.getReplyToId() == null ? Mono.<Void>empty()
+                                : access.markAnswered(request.getReplyToId(), user.getId(), login))
+                                .then(draftId == null ? Mono.<Void>empty() : mailService.finishDraft(draftId, sent.getId()))
                                 .then(mailService.getMessage(sent.getId(), user.getId()))));
     }
 
@@ -88,10 +97,10 @@ public class SubmissionService {
         for (String address : concat(to, cc)) {
             SmtpBackend.Route route = router.route(address, user.getEmail());
             switch (route) {
-                case LOCAL, OUTBOUND -> recipients.add(new SmtpBackend.Recipient(address, route));
+                case LOCAL, OUTBOUND, TRAP -> recipients.add(new SmtpBackend.Recipient(address, route));
                 case UNKNOWN_USER -> throw MailService.badRequest("No such mailbox: " + address);
                 case OUTBOUND_DISABLED -> throw MailService.badRequest("Sending outside is disabled on this server: " + address);
-                case RELAY_DENIED -> throw new IllegalStateException("logged-in user denied relay");
+                case RELAY_DENIED, LIST_CLOSED -> throw new IllegalStateException("logged-in user denied: " + route);
             }
         }
         String messageId = UUID.randomUUID() + "@" + hostname;

backend/src/main/java/com/mailserver/service/UserService.java

@@ -74,6 +74,11 @@ public class UserService {
         return userRepository.save(user).then();
     }
 
+    /** The mailbox, or empty (no error). */
+    public Mono<User> findOptional(String email) {
+        return userRepository.findByEmail(email.toLowerCase(java.util.Locale.ROOT));
+    }
+
     public Flux<User> all() {
         return userRepository.findAll();
     }
@@ -93,6 +98,16 @@ public class UserService {
         return userRepository.save(user);
     }
 
+    public Mono<User> setShared(User user, boolean shared) {
+        user.setShared(shared);
+        return userRepository.save(user);
+    }
+
+    public Mono<User> setTrap(User user, boolean trap) {
+        user.setTrap(trap);
+        return userRepository.save(user);
+    }
+
     public Mono<User> updateDisplayName(User user, String displayName) {
         user.setDisplayName(displayName.trim());
         return userRepository.save(user);

backend/src/main/java/com/mailserver/smtp/MailRouter.java

@@ -7,16 +7,26 @@ import com.mailserver.domain.User;
 import com.mailserver.repository.UserRepository;
 import com.mailserver.service.DkimService;
 import com.mailserver.service.LocalDelivery;
+import com.mailserver.service.MailLists;
+import com.mailserver.service.MailboxAccess;
 import com.mailserver.service.UserService;
 import org.springframework.stereotype.Service;
 
+import java.util.LinkedHashSet;
 import java.util.Locale;
+import java.util.Set;
 
 /**
  * Where mail goes — one rule for SMTP and for the web client:
- * an existing mailbox of our domain → that mailbox; catch-all set → everything else into the catch-all mailbox
- * (nothing goes outside, existing mailboxes still get their own mail); otherwise our domain without such a mailbox →
- * "no such user", someone else's domain → the delivery queue, only for a logged-in sender (never an open relay).
+ * <ul>
+ *   <li>a mailbox of ours → that mailbox; {@code bob+prod@} → bob's folder "prod" (created on first mail);</li>
+ *   <li>a mailing list of ours ({@code alerts-prod@}) → a copy to every member, into the list's folder
+ *       (or the "+tag" folder); a closed list takes mail only from logged-in senders;</li>
+ *   <li>a TRAP sender (staging@) and an address that is not ours → nothing leaves: one copy into the sender's INBOX
+ *       (our own mailboxes and lists still get their mail);</li>
+ *   <li>catch-all set → everything else into the catch-all mailbox; otherwise our domain → "no such user",
+ *       someone else's domain → the delivery queue, only for a logged-in sender (never an open relay).</li>
+ * </ul>
  */
 @Service
 public class MailRouter implements SmtpBackend {
@@ -28,9 +38,13 @@ public class MailRouter implements SmtpBackend {
     private final OutboundQueue queue;
     private final DkimService dkim;
     private final SmtpDeliveryClient client;
+    private final MailLists lists;
+    private final MailboxAccess access;
 
     public MailRouter(MailDomains domains, UserRepository users, UserService userService, LocalDelivery localDelivery,
-                      OutboundQueue queue, DkimService dkim, SmtpDeliveryClient client) {
+                      OutboundQueue queue, DkimService dkim, SmtpDeliveryClient client, MailLists lists,
+                      MailboxAccess access) {
+        this.access = access;
         this.domains = domains;
         this.users = users;
         this.userService = userService;
@@ -38,18 +52,29 @@ public class MailRouter implements SmtpBackend {
         this.queue = queue;
         this.dkim = dkim;
         this.client = client;
+        this.lists = lists;
     }
 
     @Override
-    public boolean authenticate(String username, String password) {
-        User user = users.findByEmail(username.toLowerCase(Locale.ROOT)).block();
-        return user != null && user.isActive() && userService.checkPassword(user, password);
+    public String authenticate(String username, String password) {
+        User mailbox = access.login(username, password);
+        return mailbox == null ? null : mailbox.getEmail();
     }
 
     @Override
     public Route route(String recipient, String authenticatedUser) {
-        if (domains.isLocal(recipient) && mailboxExists(recipient)) {
-            return Route.LOCAL;
+        if (domains.isLocal(recipient)) {
+            String base = MailDomains.baseOf(recipient);
+            if (mailboxExists(recipient) || mailboxExists(base)) {
+                return Route.LOCAL;
+            }
+            MailLists.MailList list = lists.find(base).block();
+            if (list != null) {
+                return list.openToOutside() || authenticatedUser != null ? Route.LOCAL : Route.LIST_CLOSED;
+            }
+        }
+        if (isTrap(authenticatedUser)) {
+            return Route.TRAP;
         }
         if (domains.catchAll() != null) {
             return Route.LOCAL;
@@ -66,13 +91,13 @@ public class MailRouter implements SmtpBackend {
     @Override
     public void accept(Envelope envelope, byte[] message) throws Exception {
         boolean trusted = envelope.authenticatedUser() != null;
+        // one copy per mailbox + folder, even when an address and a list both lead there
+        Set<Target> targets = new LinkedHashSet<>();
         byte[] signed = null;
         for (Recipient recipient : envelope.recipients()) {
             switch (recipient.route()) {
-                case LOCAL -> {
-                    String mailbox = mailbox(recipient.address());
-                    localDelivery.deliver(message, mailbox, envelope.remoteIp(), envelope.mailFrom(), trusted);
-                }
+                case LOCAL -> targets.addAll(targets(recipient.address()));
+                case TRAP -> targets.add(new Target(envelope.authenticatedUser().toLowerCase(Locale.ROOT), null));
                 case OUTBOUND -> {
                     if (signed == null) {
                         signed = dkim.sign(message);
@@ -82,14 +107,56 @@ public class MailRouter implements SmtpBackend {
                 default -> throw new IllegalStateException("Recipient was not accepted: " + recipient);
             }
         }
+        for (Target target : targets) {
+            localDelivery.deliver(message, target.mailbox(), target.folder(), envelope.remoteIp(), envelope.mailFrom(), trusted);
+        }
     }
 
-    /** Mailbox that stores mail to this address: its own if it exists here, otherwise the catch-all one. */
-    String mailbox(String address) {
-        if (domains.catchAll() == null || (domains.isLocal(address) && mailboxExists(address))) {
-            return address;
+    /** Mailbox + folder (null — INBOX) that store mail to a local address. */
+    record Target(String mailbox, String folder) {
+    }
+
+    Set<Target> targets(String address) {
+        Set<Target> result = new LinkedHashSet<>();
+        String lower = address.toLowerCase(Locale.ROOT);
+        if (domains.isLocal(lower)) {
+            if (mailboxExists(lower)) {
+                result.add(new Target(lower, null));
+                return result;
+            }
+            String base = MailDomains.baseOf(lower);
+            String tag = MailDomains.tagOf(address);
+            if (mailboxExists(base)) {
+                result.add(new Target(base, tag));
+                return result;
+            }
+            MailLists.MailList list = lists.find(base).block();
+            if (list != null) {
+                for (String member : list.members()) {
+                    result.add(new Target(member, tag != null ? tag : list.folder()));
+                }
+                return result;
+            }
         }
-        return domains.catchAll();
+        if (domains.catchAll() != null) {
+            result.add(new Target(domains.catchAll(), null));
+        }
+        return result;
+    }
+
+    /** Mailbox that stores mail to this address: its own (without "+tag") if it exists here, otherwise the catch-all one. */
+    String mailbox(String address) {
+        Set<Target> found = targets(address);
+        return found.isEmpty() ? address : found.iterator().next().mailbox();
+    }
+
+    /** The logged-in sender is a trap mailbox. */
+    boolean isTrap(String authenticatedUser) {
+        if (authenticatedUser == null) {
+            return false;
+        }
+        User user = users.findByEmail(authenticatedUser.toLowerCase(Locale.ROOT)).block();
+        return user != null && user.isTrap();
     }
 
     private boolean mailboxExists(String address) {

backend/src/main/java/com/mailserver/smtp/SmtpBackend.java

@@ -10,8 +10,12 @@ public interface SmtpBackend {
 
     /** Where a recipient goes, decided at RCPT TO. */
     enum Route {
-        /** A mailbox of ours (or the catch-all mailbox) — store it. */
+        /** A mailbox or mailing list of ours (or the catch-all mailbox) — store it. */
         LOCAL,
+        /** The sender is a trap mailbox and the address is not ours: one copy into the sender's own INBOX. */
+        TRAP,
+        /** A mailing list of ours that takes mail only from logged-in senders. */
+        LIST_CLOSED,
         /** Someone else's address, sender is logged in — queue for delivery. */
         OUTBOUND,
         /** Address of our domain that does not exist. */
@@ -28,8 +32,11 @@ public interface SmtpBackend {
     record Envelope(String remoteIp, String helo, String mailFrom, String authenticatedUser, List<Recipient> recipients) {
     }
 
-    /** true — the address and password belong to an active mailbox. */
-    boolean authenticate(String username, String password);
+    /**
+     * {@code login} or {@code mailbox*login} with the login's password → the mailbox address the session works as,
+     * or null.
+     */
+    String authenticate(String username, String password);
 
     Route route(String recipient, String authenticatedUser);
 

backend/src/main/java/com/mailserver/smtp/SmtpServer.java

@@ -373,12 +373,13 @@ public class SmtpServer {
                 closing = true;
                 return reply("421 4.7.0 Too many failed logins, try again in " + LoginGuard.human(wait));
             }
-            return blocking(() -> backend.authenticate(username, password))
-                    .flatMap(ok -> {
-                        if (ok) {
+            return blocking(() -> java.util.Optional.ofNullable(backend.authenticate(username, password)))
+                    .flatMap(found -> {
+                        if (found.isPresent()) {
                             guard.success(remoteIp, username);
-                            authenticatedUser = username;
-                            log.info("SMTP {}: authenticated as {}", remoteIp, username);
+                            authenticatedUser = found.get();
+                            log.info("SMTP {}: authenticated as {}{}", remoteIp, found.get(),
+                                    found.get().equalsIgnoreCase(username) ? "" : " (login " + username + ")");
                             return Mono.just("235 2.7.0 Authentication successful\r\n");
                         }
                         guard.failure(remoteIp, username);
@@ -438,7 +439,7 @@ public class SmtpServer {
             String user = authenticatedUser;
             return blocking(() -> backend.route(address, user))
                     .map(route -> switch (route) {
-                        case LOCAL, OUTBOUND -> {
+                        case LOCAL, OUTBOUND, TRAP -> {
                             recipients.add(new SmtpBackend.Recipient(address, route));
                             yield "250 2.1.5 Recipient OK\r\n";
                         }
@@ -448,6 +449,7 @@ public class SmtpServer {
                             yield "550 5.7.1 Relaying denied: authentication required\r\n";
                         }
                         case OUTBOUND_DISABLED -> "550 5.7.1 Outbound delivery is disabled on this server\r\n";
+                        case LIST_CLOSED -> "550 5.7.1 This list takes mail only from logged-in senders\r\n";
                     });
         }
 

backend/src/main/java/com/mailserver/util/JwtUtils.java

@@ -18,11 +18,20 @@ public class JwtUtils {
     }
 
     public String generateToken(String email) {
+        return generateToken(email, null);
+    }
+
+    /**
+     * @param by the login that opened this mailbox (shared / attached mailbox, administrator's OPEN), or null —
+     *           the mailbox itself logged in
+     */
+    public String generateToken(String email, String by) {
         Date now = new Date();
         Date expiry = new Date(now.getTime() + EXPIRATION_MS);
 
         return Jwts.builder()
                 .subject(email)
+                .claim("by", by)
                 .issuedAt(now)
                 .expiration(expiry)
                 .signWith(signingKey)
@@ -38,6 +47,12 @@ public class JwtUtils {
         return claims.getSubject();
     }
 
+    /** "by" claim: who opened this mailbox, or null. */
+    public String getByFromToken(String token) {
+        Object by = Jwts.parser().verifyWith(signingKey).build().parseSignedClaims(token).getPayload().get("by");
+        return by == null ? null : by.toString();
+    }
+
     public boolean isValidToken(String token) {
         try {
             Jwts.parser()

backend/src/main/resources/application.properties

@@ -31,6 +31,9 @@ mailserver.admin.password=${MAIL_ADMIN_PASSWORD:}
 mailserver.admins=${MAIL_ADMINS:}
 # Generated passwords of created mailboxes (first admin, catch-all) are appended here (mode 600); empty — printed to the log once
 mailserver.passwords-file=${MAIL_PASSWORDS_FILE:}
+# Service API for Jambotron (/api/service/**, staff mailboxes and lists); empty — the API is off.
+# In the compose files: generated by secrets-init into the secrets volume (file SERVICE_TOKEN).
+mailserver.service-token=${SERVICE_TOKEN:}
 mailserver.cors.origins=${MAIL_CORS_ORIGINS:}
 
 # Attachments

backend/src/main/resources/db/migration/V5__trap_mailbox.sql

@@ -0,0 +1,3 @@
+-- Trap mailbox: what it sends is NOT delivered to anyone — every copy lands in its own INBOX (staging@: test mail
+-- of a staging stand never reaches real people). Switched on by an administrator in Settings → MAILBOXES.
+ALTER TABLE users ADD COLUMN is_trap BOOLEAN NOT NULL DEFAULT FALSE;

backend/src/main/resources/db/migration/V6__lists.sql

@@ -0,0 +1,18 @@
+-- Mailing lists (alerts-prod@ …): mail to the list address → a copy into the mailbox of EVERY member,
+-- into the list's folder (created on first mail). Each member has their own copy — their own read/unread.
+-- open_to_outside = false: only logged-in senders (Kuma, Jambotron) may write to the list.
+CREATE TABLE mail_lists (
+    id BIGSERIAL PRIMARY KEY,
+    address VARCHAR(255) UNIQUE NOT NULL,
+    folder VARCHAR(50),
+    description VARCHAR(255),
+    open_to_outside BOOLEAN NOT NULL DEFAULT FALSE,
+    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE mail_list_members (
+    list_id BIGINT NOT NULL REFERENCES mail_lists(id) ON DELETE CASCADE,
+    user_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    PRIMARY KEY (list_id, user_id)
+);
+CREATE INDEX idx_mail_list_members_user ON mail_list_members(user_id);

backend/src/main/resources/db/migration/V7__mailbox_access.sql

@@ -0,0 +1,19 @@
+-- Several mailboxes for one login (75.9):
+--   shared mailbox (support@, billing@): no login of its own, members open it from their mailbox; read/unread is
+--   common — a team inbox; answered_by shows who replied;
+--   attached mailbox: a login adds another mailbox it knows the password of.
+ALTER TABLE users ADD COLUMN is_shared BOOLEAN NOT NULL DEFAULT FALSE;
+
+CREATE TABLE mailbox_access (
+    mailbox_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    user_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    -- MEMBER: given by an administrator / Jambotron; ATTACHED: added by the user with the mailbox password
+    kind VARCHAR(10) NOT NULL,
+    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (mailbox_id, user_id),
+    CHECK (mailbox_id <> user_id)
+);
+CREATE INDEX idx_mailbox_access_user ON mailbox_access(user_id);
+
+-- who answered a message (web client reply; mostly for shared mailboxes)
+ALTER TABLE messages ADD COLUMN answered_by VARCHAR(255);

backend/src/test/java/com/mailserver/config/MailDomainsTest.java

@@ -0,0 +1,19 @@
+package com.mailserver.config;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/** "+tag" addresses: the base address is the mailbox, the tag is the folder. */
+class MailDomainsTest {
+
+    @Test
+    void baseAndTag() {
+        assertThat(MailDomains.baseOf("Bob+Prod@Mail.test")).isEqualTo("bob@mail.test");
+        assertThat(MailDomains.tagOf("Bob+Prod@Mail.test")).isEqualTo("Prod");
+        assertThat(MailDomains.baseOf("bob@mail.test")).isEqualTo("bob@mail.test");
+        assertThat(MailDomains.tagOf("bob@mail.test")).isNull();
+        assertThat(MailDomains.tagOf("bob+@mail.test")).isNull();
+        assertThat(MailDomains.tagOf("+x@mail.test")).isNull();
+    }
+}

backend/src/test/java/com/mailserver/controller/MailboxAdminControllerTest.java

@@ -34,13 +34,24 @@ class MailboxAdminControllerTest {
     private final MailDomains domains = new MailDomains("jambocheck.com", "");
     private final MailAdmins admins = new MailAdmins("", "", domains);
     private final com.mailserver.util.JwtUtils jwt = mock(com.mailserver.util.JwtUtils.class);
-    private final MailboxAdminController controller = new MailboxAdminController(users, mail, domains, admins, jwt);
+    private final com.mailserver.service.MailLists lists = mock(com.mailserver.service.MailLists.class);
+    private final com.mailserver.service.MailboxAccess access = mock(com.mailserver.service.MailboxAccess.class);
+    private final com.mailserver.service.MailDirectory directory = new com.mailserver.service.MailDirectory(users, lists, domains, access);
+    private final MailboxAdminController controller = new MailboxAdminController(users, mail, domains, admins, jwt, directory, lists, access);
 
     private final User admin = user(1L, "admin@jambocheck.com");
     private final User alice = user(2L, "alice@jambocheck.com");
 
     MailboxAdminControllerTest() {
         when(mail.usedBytes(anyLong())).thenReturn(Mono.just(0L));
+        when(lists.exists(anyString())).thenReturn(Mono.just(false));
+        when(access.members(anyLong())).thenReturn(Flux.empty());
+        when(lists.exists("alerts@jambocheck.com")).thenReturn(Mono.just(true));
+        when(users.findOptional(anyString())).thenReturn(Mono.empty());
+        when(users.findOptional("alice@jambocheck.com")).thenReturn(Mono.just(alice));
+        when(lists.save(anyString(), any(), any(), any(Boolean.class), any())).thenAnswer(i ->
+                Mono.just(new com.mailserver.service.MailLists.MailList(5L, i.getArgument(0), i.getArgument(1), i.getArgument(2),
+                        i.getArgument(3), List.of("alice@jambocheck.com"))));
         when(users.all()).thenReturn(Flux.just(alice, admin));
         when(users.byId(1L)).thenReturn(Mono.just(admin));
         when(users.byId(2L)).thenReturn(Mono.just(alice));
@@ -52,6 +63,61 @@ class MailboxAdminControllerTest {
             u.setActive(i.getArgument(1));
             return Mono.just(u);
         });
+        when(users.setTrap(any(), any(Boolean.class))).thenAnswer(i -> {
+            User u = i.getArgument(0);
+            u.setTrap(i.getArgument(1));
+            return Mono.just(u);
+        });
+    }
+
+    @Test
+    void mailboxAndListShareOneAddressSpaceNoPlusInNames() {
+        assertThat(status(() -> create("admin@jambocheck.com", "alerts@jambocheck.com", ""))).isEqualTo(HttpStatus.CONFLICT);
+        assertThat(status(() -> create("admin@jambocheck.com", "bob+x@jambocheck.com", ""))).isEqualTo(HttpStatus.BAD_REQUEST);
+        assertThat(create("admin@jambocheck.com", "jambotron_prod@jambocheck.com", "").mailbox().email()).isEqualTo("jambotron_prod@jambocheck.com");
+
+        var request = new MailboxAdminController.ListRequest("prod", "alerts", false, List.of("Alice@jambocheck.com"));
+        assertThat(controller.saveList(as("admin@jambocheck.com"), "alerts-prod@jambocheck.com", Mono.just(request)).block().members())
+                .containsExactly("alice@jambocheck.com");
+        assertThat(status(() -> controller.saveList(as("admin@jambocheck.com"), "alice@jambocheck.com", Mono.just(request)).block()))
+                .isEqualTo(HttpStatus.CONFLICT);
+        var unknown = new MailboxAdminController.ListRequest("prod", null, false, List.of("ghost@jambocheck.com"));
+        assertThat(status(() -> controller.saveList(as("admin@jambocheck.com"), "alerts-prod@jambocheck.com", Mono.just(unknown)).block()))
+                .isEqualTo(HttpStatus.BAD_REQUEST);
+        var badFolder = new MailboxAdminController.ListRequest("Trash", null, false, List.of());
+        assertThat(status(() -> controller.saveList(as("admin@jambocheck.com"), "alerts-prod@jambocheck.com", Mono.just(badFolder)).block()))
+                .isEqualTo(HttpStatus.BAD_REQUEST);
+        assertThat(status(() -> controller.saveList(as("alice@jambocheck.com"), "alerts-prod@jambocheck.com", Mono.just(request)).block()))
+                .isEqualTo(HttpStatus.FORBIDDEN);
+    }
+
+    @Test
+    void sharedMailboxHasNoPasswordShownMembersAreSet() {
+        when(users.setShared(any(), any(Boolean.class))).thenAnswer(i -> {
+            User u = i.getArgument(0);
+            u.setShared(i.getArgument(1));
+            return Mono.just(u);
+        });
+        var created = controller.create(as("admin@jambocheck.com"),
+                Mono.just(new MailboxAdminController.CreateRequest("support@jambocheck.com", "Support", "", true))).block();
+        assertThat(created.password()).isNull();
+        assertThat(created.mailbox().shared()).isTrue();
+
+        when(access.setMembers(anyLong(), any())).thenReturn(Mono.empty());
+        controller.members(as("admin@jambocheck.com"), 2L,
+                Mono.just(new MailboxAdminController.MembersRequest(List.of("Alice@jambocheck.com")))).block();
+        verify(access).setMembers(eq(2L), eq(List.of(2L)));
+        assertThat(status(() -> controller.members(as("admin@jambocheck.com"), 2L,
+                Mono.just(new MailboxAdminController.MembersRequest(List.of("ghost@jambocheck.com")))).block())).isEqualTo(HttpStatus.BAD_REQUEST);
+    }
+
+    @Test
+    void administratorSwitchesTrapOthersCanNot() {
+        assertThat(controller.trap(as("admin@jambocheck.com"), 2L, Mono.just(new MailboxAdminController.TrapRequest(true))).block().trap()).isTrue();
+        assertThat(alice.isTrap()).isTrue();
+        assertThat(controller.trap(as("admin@jambocheck.com"), 2L, Mono.just(new MailboxAdminController.TrapRequest(false))).block().trap()).isFalse();
+        assertThat(status(() -> controller.trap(as("alice@jambocheck.com"), 2L, Mono.just(new MailboxAdminController.TrapRequest(true))).block()))
+                .isEqualTo(HttpStatus.FORBIDDEN);
     }
 
     @Test
@@ -73,14 +139,14 @@ class MailboxAdminControllerTest {
     @Test
     void createsReservedNamesWithAGeneratedPasswordShownOnce() {
         var created = controller.create(as("admin@jambocheck.com"),
-                Mono.just(new MailboxAdminController.CreateRequest(" No-Reply@JamboCheck.com ", "Jambotron", ""))).block();
+                Mono.just(new MailboxAdminController.CreateRequest(" No-Reply@JamboCheck.com ", "Jambotron", "", null))).block();
 
         assertThat(created.mailbox().email()).isEqualTo("no-reply@jambocheck.com");
         assertThat(created.password()).hasSizeGreaterThanOrEqualTo(20);
         verify(users).register(eq("no-reply@jambocheck.com"), eq(created.password()), eq("Jambotron"));
 
         var chosen = controller.create(as("admin@jambocheck.com"),
-                Mono.just(new MailboxAdminController.CreateRequest("monitor@jambocheck.com", null, "long-enough-1"))).block();
+                Mono.just(new MailboxAdminController.CreateRequest("monitor@jambocheck.com", null, "long-enough-1", null))).block();
         assertThat(chosen.password()).isNull();
     }
 
@@ -109,7 +175,7 @@ class MailboxAdminControllerTest {
 
     @Test
     void administratorOpensAnyMailboxOthersCanNot() {
-        when(jwt.generateToken("alice@jambocheck.com")).thenReturn("alice-token");
+        when(jwt.generateToken("alice@jambocheck.com", "admin@jambocheck.com")).thenReturn("alice-token");
 
         var session = controller.open(as("admin@jambocheck.com"), 2L).block();
         assertThat(session.getEmail()).isEqualTo("alice@jambocheck.com");
@@ -120,7 +186,7 @@ class MailboxAdminControllerTest {
     }
 
     private MailboxAdminController.Created create(String me, String email, String password) {
-        return controller.create(as(me), Mono.just(new MailboxAdminController.CreateRequest(email, null, password))).block();
+        return controller.create(as(me), Mono.just(new MailboxAdminController.CreateRequest(email, null, password, null))).block();
     }
 
     private static Mono<Authentication> as(String email) {

backend/src/test/java/com/mailserver/controller/ServiceControllerTest.java

@@ -0,0 +1,109 @@
+package com.mailserver.controller;
+
+import com.mailserver.config.MailDomains;
+import com.mailserver.domain.User;
+import com.mailserver.service.MailDirectory;
+import com.mailserver.service.MailLists;
+import com.mailserver.service.UserService;
+import org.junit.jupiter.api.Test;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.server.ResponseStatusException;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.catchThrowable;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyLong;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+/** Service API for Jambotron: token only; account created once with a password; switched off → out of the lists. */
+class ServiceControllerTest {
+
+    private static final String AUTH = "Bearer s3cret-token";
+
+    private final UserService users = mock(UserService.class);
+    private final MailLists lists = mock(MailLists.class);
+    private final MailDomains domains = new MailDomains("jambocheck.com", "");
+    private final com.mailserver.service.MailboxAccess access = mock(com.mailserver.service.MailboxAccess.class);
+    private final MailDirectory directory = new MailDirectory(users, lists, domains, access);
+    private final User existing = user(7L, "jambotronpw@jambocheck.com");
+
+    ServiceControllerTest() {
+        when(users.findOptional(anyString())).thenReturn(Mono.empty());
+        when(users.findOptional("jambotronpw@jambocheck.com")).thenReturn(Mono.just(existing));
+        when(lists.exists(anyString())).thenReturn(Mono.just(false));
+        when(lists.listsOf(anyLong())).thenReturn(Flux.just("alerts-prod@jambocheck.com"));
+        when(lists.removeEverywhere(anyLong())).thenReturn(Mono.just(1L));
+        when(access.removeEverywhere(anyLong())).thenReturn(Mono.just(1L));
+        when(users.register(anyString(), anyString(), any())).thenAnswer(i -> Mono.just(user(8L, i.getArgument(0))));
+        when(users.setActive(any(), any(Boolean.class))).thenAnswer(i -> {
+            User u = i.getArgument(0);
+            u.setActive(i.getArgument(1));
+            return Mono.just(u);
+        });
+        when(users.setPassword(any(), anyString())).thenAnswer(i -> Mono.just((User) i.getArgument(0)));
+    }
+
+    private ServiceController api(String token) {
+        return new ServiceController(token, users, lists, directory, access);
+    }
+
+    @Test
+    void offWithoutTokenWrongTokenRefused() {
+        assertThat(status(() -> api("").account(AUTH, "jambotronpw@jambocheck.com"))).isEqualTo(HttpStatus.NOT_FOUND);
+        assertThat(status(() -> api("s3cret-token").account("Bearer nope", "jambotronpw@jambocheck.com"))).isEqualTo(HttpStatus.UNAUTHORIZED);
+        assertThat(status(() -> api("s3cret-token").account(null, "jambotronpw@jambocheck.com"))).isEqualTo(HttpStatus.UNAUTHORIZED);
+        assertThat(api("s3cret-token").account(AUTH, "jambotronpw@jambocheck.com").block().lists())
+                .containsExactly("alerts-prod@jambocheck.com");
+    }
+
+    @Test
+    void newAccountGetsPasswordOnceExistingDoesNot() {
+        var created = api("s3cret-token").saveAccount(AUTH, "moder@jambocheck.com",
+                Mono.just(new ServiceController.AccountRequest("Moder", true))).block();
+        assertThat(created.getStatusCode().value()).isEqualTo(201);
+        assertThat(created.getBody().password()).hasSizeGreaterThan(20);
+
+        var again = api("s3cret-token").saveAccount(AUTH, "jambotronpw@jambocheck.com",
+                Mono.just(new ServiceController.AccountRequest(null, null))).block();
+        assertThat(again.getStatusCode().value()).isEqualTo(200);
+        assertThat(again.getBody().password()).isNull();
+        verify(lists, never()).removeEverywhere(anyLong());
+
+        assertThat(status(() -> api("s3cret-token").saveAccount(AUTH, "x@gmail.com", Mono.empty()))).isEqualTo(HttpStatus.BAD_REQUEST);
+    }
+
+    @Test
+    void switchedOffLeavesEveryList() {
+        var off = api("s3cret-token").saveAccount(AUTH, "jambotronpw@jambocheck.com",
+                Mono.just(new ServiceController.AccountRequest(null, false))).block();
+        assertThat(off.getBody().account().active()).isFalse();
+        verify(lists).removeEverywhere(7L);
+        verify(access).removeEverywhere(7L);
+
+        var reset = api("s3cret-token").password(AUTH, "jambotronpw@jambocheck.com").block();
+        assertThat(reset.password()).isNotBlank();
+        verify(users).setPassword(existing, reset.password());
+    }
+
+    private static HttpStatus status(Runnable call) {
+        Throwable error = catchThrowable(call::run);
+        assertThat(error).isInstanceOf(ResponseStatusException.class);
+        return HttpStatus.valueOf(((ResponseStatusException) error).getStatusCode().value());
+    }
+
+    private static User user(Long id, String email) {
+        User user = new User();
+        user.setId(id);
+        user.setEmail(email);
+        user.setPassword("hash");
+        return user;
+    }
+}

backend/src/test/java/com/mailserver/security/ActorTest.java

@@ -0,0 +1,24 @@
+package com.mailserver.security;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/** The login behind a session: own session, or a member who opened a shared mailbox. */
+class ActorTest {
+
+    @Test
+    void ownAndOpened() {
+        var own = new UsernamePasswordAuthenticationToken("bob@x", null, List.of());
+        assertThat(Actor.login(own)).isEqualTo("bob@x");
+        assertThat(Actor.opened(own)).isFalse();
+
+        var opened = new UsernamePasswordAuthenticationToken("support@x", null, List.of());
+        opened.setDetails("bob@x");
+        assertThat(Actor.login(opened)).isEqualTo("bob@x");
+        assertThat(Actor.opened(opened)).isTrue();
+    }
+}

backend/src/test/java/com/mailserver/service/DeliveryFolderTest.java

@@ -0,0 +1,21 @@
+package com.mailserver.service;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/** A "+tag" never puts mail into a system folder and never makes a strange folder name. */
+class DeliveryFolderTest {
+
+    @Test
+    void onlyPlainOwnFolderNames() {
+        assertThat(MailService.deliveryFolderName("prod")).isEqualTo("prod");
+        assertThat(MailService.deliveryFolderName("alerts.db-1")).isEqualTo("alerts.db-1");
+        assertThat(MailService.deliveryFolderName(null)).isNull();
+        assertThat(MailService.deliveryFolderName("inbox")).isNull();
+        assertThat(MailService.deliveryFolderName("Trash")).isNull();
+        assertThat(MailService.deliveryFolderName("spam")).isNull();
+        assertThat(MailService.deliveryFolderName("../x")).isNull();
+        assertThat(MailService.deliveryFolderName("a".repeat(51))).isNull();
+    }
+}

backend/src/test/java/com/mailserver/smtp/MailRouterTest.java

@@ -3,9 +3,11 @@ package com.mailserver.smtp;
 import com.mailserver.config.MailDomains;
 import com.mailserver.delivery.OutboundQueue;
 import com.mailserver.delivery.SmtpDeliveryClient;
+import com.mailserver.domain.User;
 import com.mailserver.repository.UserRepository;
 import com.mailserver.service.DkimService;
 import com.mailserver.service.LocalDelivery;
+import com.mailserver.service.MailLists;
 import com.mailserver.service.UserService;
 import org.junit.jupiter.api.Test;
 import reactor.core.publisher.Mono;
@@ -17,6 +19,7 @@ import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.ArgumentMatchers.isNull;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
@@ -29,13 +32,33 @@ class MailRouterTest {
     private final LocalDelivery localDelivery = mock(LocalDelivery.class);
     private final OutboundQueue queue = mock(OutboundQueue.class);
     private final SmtpDeliveryClient client = mock(SmtpDeliveryClient.class);
+    private final MailLists lists = mock(MailLists.class);
+
+    private SmtpDeliveryClient.Mode mode = SmtpDeliveryClient.Mode.OFF;
+
+    private static User user(String email, boolean trap) {
+        User user = new User();
+        user.setEmail(email);
+        user.setTrap(trap);
+        return user;
+    }
 
     private MailRouter router(String catchAll) {
         when(users.existsByEmail(anyString())).thenReturn(Mono.just(false));
         when(users.existsByEmail("bob@mail.test")).thenReturn(Mono.just(true));
-        when(client.mode()).thenReturn(SmtpDeliveryClient.Mode.OFF);
+        when(users.findByEmail(anyString())).thenReturn(Mono.empty());
+        when(users.findByEmail("bob@mail.test")).thenReturn(Mono.just(user("bob@mail.test", false)));
+        when(users.findByEmail("staging@mail.test")).thenReturn(Mono.just(user("staging@mail.test", true)));
+        when(users.existsByEmail("staging@mail.test")).thenReturn(Mono.just(true));
+        when(users.existsByEmail("ann@mail.test")).thenReturn(Mono.just(true));
+        when(client.mode()).thenReturn(mode);
+        when(lists.find(anyString())).thenReturn(Mono.empty());
+        when(lists.find("alerts-prod@mail.test")).thenReturn(Mono.just(new MailLists.MailList(1L, "alerts-prod@mail.test",
+                "prod", null, false, List.of("bob@mail.test", "ann@mail.test"))));
+        when(lists.find("talk@mail.test")).thenReturn(Mono.just(new MailLists.MailList(2L, "talk@mail.test",
+                null, null, true, List.of("bob@mail.test"))));
         return new MailRouter(new MailDomains("mail.test", catchAll), users, mock(UserService.class), localDelivery,
-                queue, mock(DkimService.class), client);
+                queue, mock(DkimService.class), client, lists, mock(com.mailserver.service.MailboxAccess.class));
     }
 
     @Test
@@ -61,8 +84,70 @@ class MailRouterTest {
                 new SmtpBackend.Recipient("user@gmail.com", SmtpBackend.Route.LOCAL),
                 new SmtpBackend.Recipient("bob@mail.test", SmtpBackend.Route.LOCAL))), "Subject: hi\r\n\r\nbody".getBytes());
 
-        verify(localDelivery).deliver(any(), eq("trap@mail.test"), eq("10.0.0.5"), eq("no-reply@jambotron.com"), anyBoolean());
-        verify(localDelivery).deliver(any(), eq("bob@mail.test"), eq("10.0.0.5"), eq("no-reply@jambotron.com"), anyBoolean());
+        verify(localDelivery).deliver(any(), eq("trap@mail.test"), isNull(), eq("10.0.0.5"), eq("no-reply@jambotron.com"), anyBoolean());
+        verify(localDelivery).deliver(any(), eq("bob@mail.test"), isNull(), eq("10.0.0.5"), eq("no-reply@jambotron.com"), anyBoolean());
         verify(queue, never()).enqueue(any(), any(), any());
     }
+
+    @Test
+    void trapMailboxKeepsOutsideMailButOurAddressesStillGetIt() throws Exception {
+        mode = SmtpDeliveryClient.Mode.MX;
+        MailRouter router = router("");
+
+        // an ordinary mailbox still sends outside; the trap one keeps outside mail, ours is delivered
+        assertThat(router.route("user@gmail.com", "bob@mail.test")).isEqualTo(SmtpBackend.Route.OUTBOUND);
+        assertThat(router.route("user@gmail.com", "staging@mail.test")).isEqualTo(SmtpBackend.Route.TRAP);
+        assertThat(router.route("user@gmail.com", "Staging@Mail.test")).isEqualTo(SmtpBackend.Route.TRAP);
+        assertThat(router.route("nobody@mail.test", "staging@mail.test")).isEqualTo(SmtpBackend.Route.TRAP);
+        assertThat(router.route("bob@mail.test", "staging@mail.test")).isEqualTo(SmtpBackend.Route.LOCAL);
+        assertThat(router.route("alerts-prod@mail.test", "staging@mail.test")).isEqualTo(SmtpBackend.Route.LOCAL);
+
+        router.accept(new SmtpBackend.Envelope("10.0.0.5", "staging", "staging@mail.test", "staging@mail.test", List.of(
+                new SmtpBackend.Recipient("user@gmail.com", SmtpBackend.Route.TRAP),
+                new SmtpBackend.Recipient("other@yahoo.com", SmtpBackend.Route.TRAP),
+                new SmtpBackend.Recipient("bob@mail.test", SmtpBackend.Route.LOCAL))), "Subject: hi\r\n\r\nbody".getBytes());
+
+        verify(localDelivery).deliver(any(), eq("staging@mail.test"), isNull(), eq("10.0.0.5"), eq("staging@mail.test"), eq(true));
+        verify(localDelivery).deliver(any(), eq("bob@mail.test"), isNull(), eq("10.0.0.5"), eq("staging@mail.test"), eq(true));
+        verify(queue, never()).enqueue(any(), any(), any());
+    }
+
+    @Test
+    void plusTagGoesToThatFolderOfTheMailbox() throws Exception {
+        MailRouter router = router("");
+
+        assertThat(router.route("bob+prod@mail.test", null)).isEqualTo(SmtpBackend.Route.LOCAL);
+        assertThat(router.route("nobody+prod@mail.test", null)).isEqualTo(SmtpBackend.Route.UNKNOWN_USER);
+
+        router.accept(new SmtpBackend.Envelope("10.0.0.5", "x", "a@b.c", null, List.of(
+                new SmtpBackend.Recipient("Bob+Prod@mail.test", SmtpBackend.Route.LOCAL))), "Subject: hi\r\n\r\nbody".getBytes());
+
+        verify(localDelivery).deliver(any(), eq("bob@mail.test"), eq("Prod"), eq("10.0.0.5"), eq("a@b.c"), eq(false));
+    }
+
+    @Test
+    void listGivesEveryMemberOwnCopyInTheListFolderClosedListOnlyForLoggedIn() throws Exception {
+        MailRouter router = router("");
+
+        assertThat(router.route("alerts-prod@mail.test", null)).isEqualTo(SmtpBackend.Route.LIST_CLOSED);
+        assertThat(router.route("alerts-prod@mail.test", "monitor@mail.test")).isEqualTo(SmtpBackend.Route.LOCAL);
+        assertThat(router.route("talk@mail.test", null)).isEqualTo(SmtpBackend.Route.LOCAL);
+
+        // list + one member directly: the member gets the list copy AND the direct one (different folders), once each
+        router.accept(new SmtpBackend.Envelope("10.0.0.5", "kuma", "monitor@mail.test", "monitor@mail.test", List.of(
+                new SmtpBackend.Recipient("alerts-prod@mail.test", SmtpBackend.Route.LOCAL),
+                new SmtpBackend.Recipient("ALERTS-PROD@mail.test", SmtpBackend.Route.LOCAL),
+                new SmtpBackend.Recipient("bob@mail.test", SmtpBackend.Route.LOCAL))), "Subject: down\r\n\r\nbody".getBytes());
+
+        verify(localDelivery).deliver(any(), eq("bob@mail.test"), eq("prod"), any(), any(), eq(true));
+        verify(localDelivery).deliver(any(), eq("ann@mail.test"), eq("prod"), any(), any(), eq(true));
+        verify(localDelivery).deliver(any(), eq("bob@mail.test"), isNull(), any(), any(), eq(true));
+    }
+
+    @Test
+    void listTagOverridesTheListFolder() {
+        MailRouter router = router("");
+        assertThat(router.targets("alerts-prod+db@mail.test")).containsExactly(
+                new MailRouter.Target("bob@mail.test", "db"), new MailRouter.Target("ann@mail.test", "db"));
+    }
 }

backend/src/test/java/com/mailserver/smtp/SmtpServerTest.java

@@ -43,8 +43,8 @@ class SmtpServerTest {
         volatile boolean failStore;
 
         @Override
-        public boolean authenticate(String username, String password) {
-            return password.equals(passwords.get(username));
+        public String authenticate(String username, String password) {
+            return password.equals(passwords.get(username)) ? username : null;
         }
 
         @Override

docker-compose.image.yml

@@ -19,11 +19,11 @@ services:
       - -c
       - |
         umask 077
-        for name in DB_PASSWORD JWT_SECRET; do
+        for name in DB_PASSWORD JWT_SECRET SERVICE_TOKEN; do
           [ -s /secrets/$$name ] || head -c 48 /dev/urandom | base64 | tr -dc 'A-Za-z0-9' > /secrets/$$name
         done
         # postgres reads it as uid 70, the app as uid 10001 — readable inside these containers only
-        chmod 644 /secrets/DB_PASSWORD /secrets/JWT_SECRET
+        chmod 644 /secrets/DB_PASSWORD /secrets/JWT_SECRET /secrets/SERVICE_TOKEN
     volumes:
       - secrets:/secrets
 

docker-compose.jambotron.yml

@@ -16,11 +16,11 @@ services:
       - -c
       - |
         umask 077
-        for name in DB_PASSWORD JWT_SECRET; do
+        for name in DB_PASSWORD JWT_SECRET SERVICE_TOKEN; do
           [ -s /secrets/$$name ] || head -c 48 /dev/urandom | base64 | tr -dc 'A-Za-z0-9' > /secrets/$$name
         done
         # postgres reads it as uid 70, the app as uid 10001 — readable inside these containers only
-        chmod 644 /secrets/DB_PASSWORD /secrets/JWT_SECRET
+        chmod 644 /secrets/DB_PASSWORD /secrets/JWT_SECRET /secrets/SERVICE_TOKEN
     volumes:
       - secrets:/secrets
 

docker-compose.public.yml

@@ -35,10 +35,10 @@ services:
       - -c
       - |
         umask 077
-        for name in DB_PASSWORD JWT_SECRET; do
+        for name in DB_PASSWORD JWT_SECRET SERVICE_TOKEN; do
           [ -s /secrets/$$name ] || head -c 48 /dev/urandom | base64 | tr -dc 'A-Za-z0-9' > /secrets/$$name
         done
-        chmod 644 /secrets/DB_PASSWORD /secrets/JWT_SECRET
+        chmod 644 /secrets/DB_PASSWORD /secrets/JWT_SECRET /secrets/SERVICE_TOKEN
     volumes:
       - secrets:/secrets
 

frontend/src/app/core/api.service.ts

@@ -1,7 +1,7 @@
 import { Injectable, inject } from '@angular/core';
 import { HttpClient } from '@angular/common/http';
 import { Observable } from 'rxjs';
-import { Attachment, BlacklistEntry, Contact, Draft, Folder, Mailbox, MailboxCreated, Message, Profile, ServerConfig } from './models';
+import { Attachment, BlacklistEntry, Contact, Draft, Folder, MailList, Mailbox, MailboxCreated, MailboxEntry, Message, Profile, ServerConfig } from './models';
 
 /** The mail server REST API (same origin, /api). */
 @Injectable({ providedIn: 'root' })
@@ -19,8 +19,22 @@ export class ApiService {
 
   // mailboxes — administrators only
   mailboxes(): Observable<Mailbox[]> { return this.http.get<Mailbox[]>('/api/admin/mailboxes'); }
-  createMailbox(email: string, displayName: string, password: string): Observable<MailboxCreated> {
-    return this.http.post<MailboxCreated>('/api/admin/mailboxes', { email, displayName, password });
+  createMailbox(email: string, displayName: string, password: string, shared = false): Observable<MailboxCreated> {
+    return this.http.post<MailboxCreated>('/api/admin/mailboxes', { email, displayName, password, shared });
+  }
+  setMailboxMembers(id: number, members: string[]): Observable<Mailbox> {
+    return this.http.put<Mailbox>(`/api/admin/mailboxes/${id}/members`, { members });
+  }
+  // the logged-in user's mailboxes (left menu)
+  myMailboxes(): Observable<MailboxEntry[]> { return this.http.get<MailboxEntry[]>('/api/mailboxes'); }
+  mailboxSession(email: string): Observable<{ token: string; email: string }> {
+    return this.http.post<{ token: string; email: string }>(`/api/mailboxes/${encodeURIComponent(email)}/session`, {});
+  }
+  attachMailbox(email: string, password: string): Observable<MailboxEntry> {
+    return this.http.post<MailboxEntry>('/api/mailboxes/attach', { email, password });
+  }
+  leaveMailbox(email: string): Observable<void> {
+    return this.http.delete<void>(`/api/mailboxes/${encodeURIComponent(email)}`);
   }
   newMailboxPassword(id: number): Observable<MailboxCreated> {
     return this.http.post<MailboxCreated>(`/api/admin/mailboxes/${id}/password`, {});
@@ -28,6 +42,16 @@ export class ApiService {
   openMailbox(id: number): Observable<{ token: string; email: string }> {
     return this.http.post<{ token: string; email: string }>(`/api/admin/mailboxes/${id}/open`, {});
   }
+  mailLists(): Observable<MailList[]> { return this.http.get<MailList[]>('/api/admin/mailboxes/lists'); }
+  saveMailList(address: string, list: { folder: string; description: string; openToOutside: boolean; members: string[] }): Observable<MailList> {
+    return this.http.put<MailList>(`/api/admin/mailboxes/lists/${encodeURIComponent(address)}`, list);
+  }
+  deleteMailList(address: string): Observable<void> {
+    return this.http.delete<void>(`/api/admin/mailboxes/lists/${encodeURIComponent(address)}`);
+  }
+  setMailboxTrap(id: number, trap: boolean): Observable<Mailbox> {
+    return this.http.put<Mailbox>(`/api/admin/mailboxes/${id}/trap`, { trap });
+  }
   setMailboxActive(id: number, active: boolean): Observable<Mailbox> {
     return this.http.put<Mailbox>(`/api/admin/mailboxes/${id}/active`, { active });
   }
@@ -57,8 +81,8 @@ export class ApiService {
   // compose
   createDraft(draft: Draft): Observable<Message> { return this.http.post<Message>('/api/drafts', draft); }
   updateDraft(id: number, draft: Draft): Observable<Message> { return this.http.put<Message>(`/api/drafts/${id}`, draft); }
-  send(draft: Draft, draftId: number | null): Observable<Message> {
-    return this.http.post<Message>('/api/send', { ...draft, draftId });
+  send(draft: Draft, draftId: number | null, replyToId: number | null = null): Observable<Message> {
+    return this.http.post<Message>('/api/send', { ...draft, draftId, replyToId });
   }
 
   // attachments

frontend/src/app/core/auth.service.ts

@@ -40,6 +40,18 @@ export class AuthService {
     this.openedBy.set(read('adminEmail'));
   }
 
+  /**
+   * Switch to another mailbox of the same login (left menu). Going back to the mailbox an administrator came
+   * from ends the administrator's visit.
+   */
+  switchTo(response: TokenResponse): void {
+    if (this.openedBy() && response.email === this.openedBy()) {
+      this.backToAdmin();
+      return;
+    }
+    this.store(response);
+  }
+
   /** Back to the administrator's own mailbox. */
   backToAdmin(): void {
     const token = read('adminToken');

frontend/src/app/core/models.ts

@@ -23,6 +23,16 @@ export interface Message {
   receivedAt: string;
   hasAttachments: boolean;
   attachmentCount: number;
+  answeredBy?: string | null;   // login that answered it from the web client (shared mailboxes)
+}
+
+/** MailboxAccess.Entry — a mailbox of the logged-in user (left menu) */
+export interface MailboxEntry {
+  email: string;
+  displayName: string;
+  kind: 'OWN' | 'MEMBER' | 'ATTACHED';
+  shared: boolean;
+  unread: number;
 }
 
 export interface Attachment {
@@ -63,11 +73,24 @@ export interface Mailbox {
   displayName: string;
   active: boolean;
   admin: boolean;
+  trap: boolean;          // what it sends to outside addresses stays in its own INBOX (staging@)
+  shared: boolean;        // shared mailbox: no login of its own, members open it
+  members: string[];      // who may open it
   usedBytes: number;
   quotaBytes: number;
   createdAt: string;
 }
 
+/** MailLists.MailList — mail to the address → a copy to every member, into the folder (null — INBOX) */
+export interface MailList {
+  id: number;
+  address: string;
+  folder: string | null;
+  description: string | null;
+  openToOutside: boolean;
+  members: string[];
+}
+
 /** password — generated by the server, shown once; null when the administrator chose it */
 export interface MailboxCreated {
   mailbox: Mailbox;

frontend/src/app/pages/compose/compose.page.ts

@@ -141,6 +141,8 @@ export class ComposePage {
   readonly body = signal('');
   readonly showCc = signal(false);
   readonly draftId = signal<number | null>(null);
+  /** the message being answered: marked answered (and by whom) when this one is sent */
+  private replyToId: number | null = null;
   readonly attachments = signal<Attachment[]>([]);
   readonly dirty = signal(false);
   readonly saving = signal(false);
@@ -207,6 +209,7 @@ export class ComposePage {
   }
 
   private fromReply(m: Message, all: boolean): void {
+    this.replyToId = m.id;
     const me = (this.state.profile()?.email ?? '').toLowerCase();
     this.to.set(m.senderEmail);
     if (all) {
@@ -306,7 +309,7 @@ export class ComposePage {
     const go = () => {
       this.sending.set(true);
       this.error.set('');
-      this.api.send(this.current(), this.draftId()).subscribe({
+      this.api.send(this.current(), this.draftId(), this.replyToId).subscribe({
         next: () => {
           this.done = true;
           this.toasts.ok('Message sent');

frontend/src/app/pages/message/message.page.ts

@@ -73,6 +73,10 @@ import { ToastService } from '../../ui/toast.service';
             }
             <dt class="text-slate-500 font-mono text-xs pt-0.5">Date</dt>
             <dd class="text-slate-400 font-mono text-xs pt-0.5">{{ m.receivedAt | date: 'EEEE, d MMMM y, HH:mm' }}</dd>
+            @if (m.answeredBy) {
+              <dt class="text-slate-500 font-mono text-xs pt-0.5">Answered</dt>
+              <dd class="text-emerald-300 font-mono text-xs pt-0.5 flex items-center gap-1"><mat-icon class="!text-sm">reply</mat-icon> by {{ m.answeredBy }}</dd>
+            }
           </dl>
         </div>
 

frontend/src/app/pages/settings/lists.section.ts

@@ -0,0 +1,154 @@
+import { ChangeDetectionStrategy, Component, computed, inject, signal } from '@angular/core';
+import { FormsModule } from '@angular/forms';
+import { MatIconModule } from '@angular/material/icon';
+import { ApiService } from '../../core/api.service';
+import { MailList, Mailbox, errorText } from '../../core/models';
+import { ToastService } from '../../ui/toast.service';
+
+/**
+ * Settings → LISTS (administrators): alerts-prod@ → a copy to every member, into the list's folder.
+ * Lists kept by Jambotron are edited here too, but Jambotron puts its own member set back on its next sync.
+ */
+@Component({
+  selector: 'app-lists-section',
+  imports: [FormsModule, MatIconModule],
+  changeDetection: ChangeDetectionStrategy.OnPush,
+  host: { class: 'block xl:col-span-2' },
+  template: `
+    <section class="glass-panel static p-5 md:p-6" aria-labelledby="lists-title">
+      <h2 id="lists-title" class="text-lg font-orbitron font-bold text-cyan-300 flex items-center gap-2 mb-2 border-b border-cyan-500/20 pb-2">
+        <mat-icon class="text-pink-500">forward_to_inbox</mat-icon> LISTS
+      </h2>
+      <p class="text-xs text-slate-400 mb-4">
+        Mail to a list goes to every member — each gets their own copy (own read/unread) in the list's folder.
+        <span class="font-mono">list+tag&#64;</span> puts it into folder «tag» instead. Closed list: only logged-in senders (Kuma, Jambotron).
+      </p>
+
+      <form (ngSubmit)="save()" class="grid grid-cols-1 md:grid-cols-[1fr_1fr_1fr] gap-3 mb-3">
+        <div><label class="synth-label" for="ls-address">Address</label>
+          <div class="flex items-stretch gap-2">
+            <input id="ls-address" name="address" class="synth-input" [ngModel]="local()" (ngModelChange)="local.set($event.toLowerCase().trim())"
+                   placeholder="alerts-prod" autocomplete="off" required [readonly]="editing()">
+            <span class="flex items-center text-cyan-300 font-mono">&#64;</span>
+            <span class="flex items-center px-3 rounded-[10px] bg-slate-900/70 border border-cyan-500/30 font-mono text-sm text-slate-200 whitespace-nowrap">{{ domain() }}</span>
+          </div></div>
+        <div><label class="synth-label" for="ls-folder">Folder (empty — INBOX)</label>
+          <input id="ls-folder" name="folder" class="synth-input" [(ngModel)]="folder" maxlength="50" placeholder="prod" autocomplete="off"></div>
+        <div><label class="synth-label" for="ls-about">Description</label>
+          <input id="ls-about" name="about" class="synth-input" [(ngModel)]="description" maxlength="255" autocomplete="off"></div>
+        <fieldset class="md:col-span-3">
+          <legend class="synth-label">Members</legend>
+          <div class="flex flex-wrap gap-x-4 gap-y-1">
+            @for (m of mailboxes(); track m.id) {
+              <label class="flex items-center gap-1.5 text-sm font-mono" [class.text-slate-500]="!m.active">
+                <input type="checkbox" [checked]="members().has(m.email)" (change)="flip(m.email)"> {{ m.email }}
+              </label>
+            }
+          </div>
+        </fieldset>
+        <div class="md:col-span-3 flex flex-wrap items-center gap-3">
+          <label class="flex items-center gap-1.5 text-sm"><input type="checkbox" name="open" [(ngModel)]="openToOutside"> open to anyone (not only logged-in senders)</label>
+          <span class="ml-auto"></span>
+          @if (editing()) { <button type="button" class="ghost-btn !py-1" (click)="reset()"><mat-icon>close</mat-icon> CANCEL</button> }
+          <button type="submit" class="cyber-btn px-4 py-2 rounded-lg text-xs font-bold" [disabled]="busy()">
+            <mat-icon>{{ editing() ? 'save' : 'add' }}</mat-icon> {{ editing() ? 'SAVE' : 'CREATE' }}</button>
+        </div>
+      </form>
+      @if (error()) { <p class="text-sm text-pink-400 mb-3" role="alert">{{ error() }}</p> }
+
+      <ul class="divide-y divide-cyan-500/10">
+        @for (l of lists(); track l.id) {
+          <li class="py-2">
+            <div class="flex flex-wrap items-center gap-x-4 gap-y-1">
+              <span class="font-mono text-sm text-cyan-300">{{ l.address }}</span>
+              <span class="text-xs font-mono text-slate-400">→ {{ l.folder || 'INBOX' }}</span>
+              @if (l.openToOutside) { <span class="text-[10px] font-mono px-1.5 rounded border border-amber-400/50 text-amber-300">OPEN</span> }
+              <span class="text-sm text-slate-400">{{ l.description }}</span>
+              <span class="ml-auto"></span>
+              <button type="button" class="ghost-btn !py-1" (click)="edit(l)" [attr.aria-label]="'Edit ' + l.address"><mat-icon>edit</mat-icon></button>
+              <button type="button" class="ghost-btn !py-1" (click)="remove(l)" [attr.aria-label]="'Delete ' + l.address"><mat-icon>delete</mat-icon></button>
+            </div>
+            <div class="text-xs font-mono text-slate-500 mt-0.5">{{ l.members.length ? l.members.join(', ') : 'no members — mail to it is dropped' }}</div>
+          </li>
+        } @empty {
+          <li class="py-2 text-sm text-slate-500">No lists yet.</li>
+        }
+      </ul>
+    </section>
+  `
+})
+export class ListsSection {
+  private api = inject(ApiService);
+  private toasts = inject(ToastService);
+
+  readonly lists = signal<MailList[]>([]);
+  readonly mailboxes = signal<Mailbox[]>([]);
+  readonly members = signal<Set<string>>(new Set());
+  readonly local = signal('');
+  readonly domains = signal<string[]>([]);
+  readonly domain = computed(() => this.domains()[0] ?? '');
+  readonly editing = signal(false);
+  readonly error = signal('');
+  readonly busy = signal(false);
+  folder = '';
+  description = '';
+  openToOutside = false;
+
+  constructor() {
+    this.api.config().subscribe({ next: c => this.domains.set(c.domains), error: () => {} });
+    this.api.mailboxes().subscribe({ next: list => this.mailboxes.set(list), error: () => {} });
+    this.load();
+  }
+
+  load(): void {
+    this.api.mailLists().subscribe({ next: list => this.lists.set(list), error: e => this.error.set(errorText(e)) });
+  }
+
+  flip(email: string): void {
+    const next = new Set(this.members());
+    if (next.has(email)) { next.delete(email); } else { next.add(email); }
+    this.members.set(next);
+  }
+
+  edit(l: MailList): void {
+    this.local.set(l.address.split('@')[0]);
+    this.domains.set([l.address.split('@')[1], ...this.domains().filter(d => d !== l.address.split('@')[1])]);
+    this.folder = l.folder ?? '';
+    this.description = l.description ?? '';
+    this.openToOutside = l.openToOutside;
+    this.members.set(new Set(l.members));
+    this.editing.set(true);
+    this.error.set('');
+  }
+
+  reset(): void {
+    this.local.set('');
+    this.folder = this.description = '';
+    this.openToOutside = false;
+    this.members.set(new Set());
+    this.editing.set(false);
+  }
+
+  save(): void {
+    const local = this.local().replace(/@.*$/, '');
+    if (!local) { this.error.set('Enter an address'); return; }
+    const address = local + '@' + this.domain();
+    this.error.set('');
+    this.busy.set(true);
+    this.api.saveMailList(address, {
+      folder: this.folder.trim(), description: this.description.trim(), openToOutside: this.openToOutside,
+      members: [...this.members()]
+    }).subscribe({
+      next: saved => { this.busy.set(false); this.toasts.ok('List ' + saved.address + ' saved'); this.reset(); this.load(); },
+      error: e => { this.busy.set(false); this.error.set(errorText(e)); }
+    });
+  }
+
+  remove(l: MailList): void {
+    if (!confirm('Delete list ' + l.address + '? Mail to it will be refused.')) return;
+    this.api.deleteMailList(l.address).subscribe({
+      next: () => { this.toasts.ok('List ' + l.address + ' deleted'); this.load(); },
+      error: e => this.toasts.error(errorText(e))
+    });
+  }
+}

frontend/src/app/pages/settings/mailboxes.section.ts

@@ -43,6 +43,10 @@ import { AuthService } from '../../core/auth.service';
               <mat-icon>{{ showPw() ? 'visibility_off' : 'visibility' }}</mat-icon>
             </button></div></div>
         <button type="submit" class="cyber-btn px-4 py-2 rounded-lg text-xs font-bold" [disabled]="busy()"><mat-icon>add</mat-icon> CREATE</button>
+        <label class="md:col-span-4 flex items-center gap-1.5 text-sm text-slate-300">
+          <input type="checkbox" name="shared" [(ngModel)]="shared">
+          shared mailbox (support&#64;, billing&#64;): no password of its own — members open it from their mailbox, read/unread is common
+        </label>
       </form>
       @if (error()) { <p class="text-sm text-pink-400 mb-3" role="alert">{{ error() }}</p> }
 
@@ -63,17 +67,49 @@ import { AuthService } from '../../core/auth.service';
             <span class="font-mono text-sm" [class.text-cyan-300]="m.active" [class.text-slate-500]="!m.active" [class.line-through]="!m.active">{{ m.email }}</span>
             <span class="text-sm text-slate-400">{{ m.displayName }}</span>
             @if (m.admin) { <span class="text-[10px] font-mono px-1.5 rounded border border-pink-500/40 text-pink-300">ADMIN</span> }
+            @if (m.shared) { <span class="text-[10px] font-mono px-1.5 rounded border border-cyan-400/50 text-cyan-300"
+                                   [title]="'Members: ' + (m.members.join(', ') || 'none')">SHARED · {{ m.members.length }}</span> }
+            @if (!m.shared && m.members.length) { <span class="text-[10px] font-mono px-1.5 rounded border border-cyan-400/30 text-cyan-300/80"
+                                   [title]="'Also opened by: ' + m.members.join(', ')">+{{ m.members.length }}</span> }
+            @if (m.trap) { <span class="text-[10px] font-mono px-1.5 rounded border border-amber-400/50 text-amber-300"
+                                 title="What it sends is kept in its own INBOX — nothing leaves the server">TRAP</span> }
             <span class="text-xs font-mono text-slate-500 ml-auto">{{ size(m.usedBytes) }}</span>
             @if (m.email !== me()) {
               <button type="button" class="ghost-btn !py-1" (click)="open(m)" [attr.aria-label]="'Open ' + m.email" title="Open mailbox">
                 <mat-icon>mark_email_read</mat-icon> OPEN</button>
             }
-            <button type="button" class="ghost-btn !py-1" (click)="newPassword(m)" [attr.aria-label]="'New password for ' + m.email"><mat-icon>key</mat-icon></button>
+            <button type="button" class="ghost-btn !py-1" (click)="editMembers(m)" [attr.aria-expanded]="membersOf() === m.id"
+                    [attr.aria-label]="'Who may open ' + m.email" title="Who may open this mailbox"><mat-icon>group</mat-icon></button>
+            <button type="button" class="ghost-btn !py-1" (click)="trap(m)" [class.text-amber-300]="m.trap"
+                    [attr.aria-label]="(m.trap ? 'Trap off for ' : 'Trap on for ') + m.email"
+                    [title]="m.trap ? 'Trap ON: sent mail stays in its INBOX. Click to send for real' : 'Trap: keep what it sends in its own INBOX'">
+              <mat-icon>{{ m.trap ? 'move_to_inbox' : 'outbox' }}</mat-icon></button>
+            @if (!m.shared) {
+              <button type="button" class="ghost-btn !py-1" (click)="newPassword(m)" [attr.aria-label]="'New password for ' + m.email"><mat-icon>key</mat-icon></button>
+            }
             @if (m.email !== me()) {
               <button type="button" class="ghost-btn !py-1" (click)="toggle(m)"
                       [attr.aria-label]="(m.active ? 'Switch off ' : 'Switch on ') + m.email">
                 <mat-icon>{{ m.active ? 'toggle_on' : 'toggle_off' }}</mat-icon></button>
             }
+            @if (membersOf() === m.id) {
+              <div class="basis-full mt-1 p-2 rounded-lg border border-cyan-500/20">
+                <div class="text-xs text-slate-400 mb-1">Who may open <span class="font-mono text-cyan-300">{{ m.email }}</span> from their own mailbox:</div>
+                <div class="flex flex-wrap gap-x-4 gap-y-1">
+                  @for (o of mailboxes(); track o.id) {
+                    @if (o.id !== m.id && !o.shared) {
+                      <label class="flex items-center gap-1.5 text-sm font-mono">
+                        <input type="checkbox" [checked]="picked().has(o.email)" (change)="pick(o.email)"> {{ o.email }}
+                      </label>
+                    }
+                  }
+                </div>
+                <div class="flex gap-2 mt-2">
+                  <button type="button" class="cyber-btn px-3 py-1 rounded-lg text-xs font-bold" (click)="saveMembers(m)"><mat-icon>save</mat-icon> SAVE</button>
+                  <button type="button" class="ghost-btn !py-1" (click)="membersOf.set(null)">CANCEL</button>
+                </div>
+              </div>
+            }
           </li>
         }
       </ul>
@@ -98,6 +134,10 @@ export class MailboxesSection {
   readonly domain = signal('');
   name = '';
   password = '';
+  shared = false;
+  /** mailbox whose members are being edited */
+  readonly membersOf = signal<number | null>(null);
+  readonly picked = signal<Set<string>>(new Set());
 
   constructor() {
     this.domain.set(this.me().split('@')[1] ?? '');
@@ -122,11 +162,12 @@ export class MailboxesSection {
     const email = local + '@' + this.domain();
     this.error.set('');
     this.busy.set(true);
-    this.api.createMailbox(email, this.name.trim(), this.password).subscribe({
+    this.api.createMailbox(email, this.name.trim(), this.password, this.shared).subscribe({
       next: created => {
         this.busy.set(false);
         this.local.set('');
         this.name = this.password = '';
+        this.shared = false;
         if (created.password) { this.secret.set({ email: created.mailbox.email, password: created.password }); }
         this.toasts.ok('Mailbox ' + created.mailbox.email + ' created');
         this.load();
@@ -151,6 +192,34 @@ export class MailboxesSection {
     });
   }
 
+  /** Trap on: what the mailbox sends is kept in its own INBOX (staging@). Off: it sends for real again. */
+  trap(m: Mailbox): void {
+    if (m.trap && !confirm('Switch the trap off? ' + m.email + ' will send mail to real people again.')) return;
+    this.api.setMailboxTrap(m.id, !m.trap).subscribe({
+      next: () => { this.toasts.ok('Trap ' + (m.trap ? 'off' : 'on') + ' for ' + m.email); this.load(); },
+      error: e => this.toasts.error(errorText(e))
+    });
+  }
+
+  editMembers(m: Mailbox): void {
+    if (this.membersOf() === m.id) { this.membersOf.set(null); return; }
+    this.picked.set(new Set(m.members));
+    this.membersOf.set(m.id);
+  }
+
+  pick(email: string): void {
+    const next = new Set(this.picked());
+    if (next.has(email)) { next.delete(email); } else { next.add(email); }
+    this.picked.set(next);
+  }
+
+  saveMembers(m: Mailbox): void {
+    this.api.setMailboxMembers(m.id, [...this.picked()]).subscribe({
+      next: () => { this.toasts.ok('Members of ' + m.email + ' saved'); this.membersOf.set(null); this.load(); },
+      error: e => this.toasts.error(errorText(e))
+    });
+  }
+
   toggle(m: Mailbox): void {
     this.api.setMailboxActive(m.id, !m.active).subscribe({
       next: () => this.load(),

frontend/src/app/pages/settings/settings.page.ts

@@ -8,11 +8,12 @@ import { errorText, formatBytes } from '../../core/models';
 import { THEMES, ThemeService } from '../../ui/theme.service';
 import { ToastService } from '../../ui/toast.service';
 import { MailboxesSection } from './mailboxes.section';
+import { ListsSection } from './lists.section';
 
 /** Profile name, password, storage, look. */
 @Component({
   selector: 'app-settings',
-  imports: [DatePipe, FormsModule, MatIconModule, MailboxesSection],
+  imports: [DatePipe, FormsModule, MatIconModule, MailboxesSection, ListsSection],
   changeDetection: ChangeDetectionStrategy.OnPush,
   template: `
     <div class="grid grid-cols-1 xl:grid-cols-2 gap-5">
@@ -113,6 +114,7 @@ import { MailboxesSection } from './mailboxes.section';
 
       @if (state.profile()?.admin) {
         <app-mailboxes-section />
+        <app-lists-section />
       }
     </div>
   `

frontend/src/app/pages/shell/shell.component.ts

@@ -8,7 +8,7 @@ import { filter } from 'rxjs';
 import { ApiService } from '../../core/api.service';
 import { AuthService } from '../../core/auth.service';
 import { MailStateService } from '../../core/mail-state.service';
-import { Folder, errorText, folderIcon, folderLabel, formatBytes } from '../../core/models';
+import { Folder, MailboxEntry, errorText, folderIcon, folderLabel, formatBytes } from '../../core/models';
 import { BackgroundComponent } from '../../ui/background.component';
 import { DialogService } from '../../ui/dialog.service';
 import { THEMES, ThemeService } from '../../ui/theme.service';
@@ -81,6 +81,44 @@ import { ToastService } from '../../ui/toast.service';
       <div class="flex-grow max-w-[1500px] w-full mx-auto p-3 md:p-5 grid grid-cols-1 lg:grid-cols-[260px_1fr] gap-5">
         <nav class="glass-panel static p-4 md:pt-6 h-fit lg:sticky lg:top-20 lg:block" [class.hidden]="!menuOpen()"
              aria-label="Mail folders">
+          <div class="flex items-center justify-between mb-2 px-1">
+            <h2 class="text-[11px] font-orbitron font-bold text-cyan-300 tracking-widest">MAILBOXES</h2>
+            <button type="button" class="text-slate-400 hover:text-cyan-300" matTooltip="Add a mailbox you have the password of"
+                    aria-label="Add mailbox" [attr.aria-expanded]="attachOpen()" (click)="attachOpen.set(!attachOpen())">
+              <mat-icon class="!text-xl">add_circle_outline</mat-icon></button>
+          </div>
+          <ul class="space-y-1 mb-3" aria-label="Your mailboxes">
+            @for (b of boxes(); track b.email) {
+              <li class="flex items-center gap-1">
+                <button type="button" (click)="switchTo(b)" [attr.aria-current]="b.email === auth.email() ? 'true' : null"
+                        class="flex-grow flex items-center gap-2 px-3 py-1.5 rounded-lg border text-left font-rajdhani font-semibold min-w-0"
+                        [class.border-pink-500/40]="b.email === auth.email()" [class.bg-pink-500/15]="b.email === auth.email()"
+                        [class.text-pink-200]="b.email === auth.email()" [class.border-transparent]="b.email !== auth.email()"
+                        [class.text-slate-300]="b.email !== auth.email()"
+                        [matTooltip]="b.email + (b.shared ? ' — shared' : b.kind === 'ATTACHED' ? ' — attached' : '')">
+                  <mat-icon class="!text-lg shrink-0">{{ b.shared ? 'groups' : b.kind === 'OWN' ? 'person' : 'link' }}</mat-icon>
+                  <span class="flex-grow truncate text-sm">{{ b.email }}</span>
+                  @if (b.unread) {
+                    <span class="text-[11px] font-mono px-2 rounded-full bg-pink-500/25 text-pink-300" [attr.aria-label]="b.unread + ' unread'">{{ b.unread }}</span>
+                  }
+                </button>
+                @if (b.kind !== 'OWN') {
+                  <button type="button" class="text-slate-500 hover:text-pink-400" [attr.aria-label]="'Remove ' + b.email + ' from my mailboxes'"
+                          matTooltip="Remove from my mailboxes" (click)="leave(b)"><mat-icon class="!text-base">close</mat-icon></button>
+                }
+              </li>
+            }
+          </ul>
+          @if (attachOpen()) {
+            <form class="space-y-2 mb-4 p-2 rounded-lg border border-cyan-500/20" (ngSubmit)="attach()" aria-label="Add a mailbox">
+              <label class="synth-label" for="att-email">Mailbox</label>
+              <input id="att-email" name="attEmail" class="synth-input !py-1.5" [(ngModel)]="attachEmail" autocomplete="off" placeholder="name&#64;domain">
+              <label class="synth-label" for="att-pw">Its password</label>
+              <input id="att-pw" name="attPw" type="password" class="synth-input !py-1.5" [(ngModel)]="attachPassword" autocomplete="off">
+              <button type="submit" class="cyber-btn w-full py-1.5 rounded-lg text-xs font-bold"><mat-icon>link</mat-icon> ADD</button>
+            </form>
+          }
+
           <a routerLink="/compose" class="cyber-btn w-full py-2.5 rounded-xl font-bold text-xs mb-4" (click)="menuOpen.set(false)">
             <mat-icon>edit</mat-icon> COMPOSE
           </a>
@@ -165,6 +203,11 @@ export class ShellComponent {
 
   readonly themes = THEMES;
   readonly menuOpen = signal(false);
+  /** own, shared and attached mailboxes of the login (shown when there is more than the own one, or to add one) */
+  readonly boxes = signal<MailboxEntry[]>([]);
+  readonly attachOpen = signal(false);
+  attachEmail = '';
+  attachPassword = '';
   query = '';
 
   readonly links = [
@@ -195,7 +238,8 @@ export class ShellComponent {
   constructor() {
     this.state.refreshFolders();
     this.state.refreshProfile();
-    const timer = setInterval(() => this.state.refreshFolders(), 30000);
+    this.loadBoxes();
+    const timer = setInterval(() => { this.state.refreshFolders(); this.loadBoxes(); }, 30000);
     inject(DestroyRef).onDestroy(() => clearInterval(timer));
     this.router.events.pipe(filter(e => e instanceof NavigationEnd)).subscribe(() => {
       const q = this.router.parseUrl(this.router.url).queryParams['q'];
@@ -256,6 +300,52 @@ export class ShellComponent {
     }
   }
 
+  loadBoxes(): void {
+    this.api.myMailboxes().subscribe({ next: list => this.boxes.set(list), error: () => {} });
+  }
+
+  /** Another mailbox of this login: its session, full reload — fresh folders and profile. */
+  switchTo(b: MailboxEntry): void {
+    if (b.email === this.auth.email()) { this.router.navigate(['/']); return; }
+    this.api.mailboxSession(b.email).subscribe({
+      next: session => { this.state.reset(); this.auth.switchTo(session); location.assign('/'); },
+      error: e => this.toasts.error(errorText(e))
+    });
+  }
+
+  attach(): void {
+    const email = this.attachEmail.trim().toLowerCase();
+    if (!email || !this.attachPassword) { this.toasts.error('Mailbox and its password'); return; }
+    this.api.attachMailbox(email, this.attachPassword).subscribe({
+      next: b => {
+        this.attachEmail = this.attachPassword = '';
+        this.attachOpen.set(false);
+        this.toasts.ok(b.email + ' added to your mailboxes');
+        this.loadBoxes();
+      },
+      error: e => this.toasts.error(errorText(e))
+    });
+  }
+
+  leave(b: MailboxEntry): void {
+    this.dialogs.confirm(`Remove ${b.email}?`, b.shared
+      ? 'It disappears from your menu. An administrator can give it back.'
+      : 'It disappears from your menu. Add it again with its password.', 'Remove', true).subscribe(ok => {
+      if (ok === null) return;
+      this.api.leaveMailbox(b.email).subscribe({
+        next: () => {
+          this.toasts.ok(b.email + ' removed');
+          if (b.email === this.auth.email()) {
+            const own = this.boxes().find(x => x.kind === 'OWN');
+            if (own) { this.switchTo(own); return; }
+          }
+          this.loadBoxes();
+        },
+        error: e => this.toasts.error(errorText(e))
+      });
+    });
+  }
+
   backToAdmin(): void {
     this.auth.backToAdmin();
     location.assign('/settings');