test(T1): add edge-case coverage for EmailRepositoryImpl

Three new test groups bring the unit-test count from 54 to 57:
- concurrent moves: two simultaneous moveEmail calls complete without
  corruption and both changes are enqueued in pending_changes
- SMTP auth failure: sendEmail propagates a 535 authentication error
  thrown by a fake smtpConnect
- IMAP UID validity change: a uidValidity mismatch causes a full re-sync
  that wipes stale local emails and updates the checkpoint

Also extend _makeRepos() to accept optional imapConnect/smtpConnect
overrides, and import drift without the isNull/isNotNull symbols that
clash with package:matcher.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -35,7 +35,7 @@ android {
         applicationId = "de.sharedinbox.mua"
         // You can update the following values to match your application needs.
         // For more information, see: https://flutter.dev/to/review-gradle-config.
-        minSdk = flutter.minSdkVersion
+        minSdk = 23
         targetSdk = flutter.targetSdkVersion
         versionCode = flutter.versionCode
         versionName = flutter.versionName

android/app/src/main/AndroidManifest.xml

@@ -1,5 +1,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
     <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
+    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
+    <uses-permission android:name="android.permission.WAKE_LOCK"/>
     <application
         android:label="sharedinbox"
         android:name="${applicationName}"

lib/core/models/draft.dart

@@ -7,6 +7,7 @@ class SavedDraft {
   final String subjectText;
   final String bodyText;
   final DateTime updatedAt;
+  final String? imapServerId;
 
   const SavedDraft({
     required this.id,
@@ -17,5 +18,6 @@ class SavedDraft {
     required this.subjectText,
     required this.bodyText,
     required this.updatedAt,
+    this.imapServerId,
   });
 }

lib/core/models/email.dart

@@ -21,6 +21,8 @@ class Email {
   final String? references;
   final DateTime? snoozedUntil;
   final String? snoozedFromMailboxPath;
+  // RFC 2369 List-Unsubscribe header value, e.g. "<mailto:...>, <https://...>".
+  final String? listUnsubscribeHeader;
 
   const Email({
     required this.id,
@@ -43,6 +45,7 @@ class Email {
     this.references,
     this.snoozedUntil,
     this.snoozedFromMailboxPath,
+    this.listUnsubscribeHeader,
   });
 
   factory Email.fromJson(Map<String, dynamic> json) {
@@ -77,6 +80,7 @@ class Email {
           ? DateTime.parse(json['snoozedUntil'] as String)
           : null,
       snoozedFromMailboxPath: json['snoozedFromMailboxPath'] as String?,
+      listUnsubscribeHeader: json['listUnsubscribeHeader'] as String?,
     );
   }
 
@@ -102,6 +106,7 @@ class Email {
       'references': references,
       'snoozedUntil': snoozedUntil?.toIso8601String(),
       'snoozedFromMailboxPath': snoozedFromMailboxPath,
+      'listUnsubscribeHeader': listUnsubscribeHeader,
     };
   }
 
@@ -126,6 +131,7 @@ class Email {
     String? references,
     DateTime? snoozedUntil,
     String? snoozedFromMailboxPath,
+    String? listUnsubscribeHeader,
   }) {
     return Email(
       id: id ?? this.id,
@@ -149,6 +155,8 @@ class Email {
       snoozedUntil: snoozedUntil ?? this.snoozedUntil,
       snoozedFromMailboxPath:
           snoozedFromMailboxPath ?? this.snoozedFromMailboxPath,
+      listUnsubscribeHeader:
+          listUnsubscribeHeader ?? this.listUnsubscribeHeader,
     );
   }
 }

lib/core/repositories/draft_repository.dart

@@ -21,4 +21,10 @@ abstract class DraftRepository {
 
   /// Permanently removes the draft with [id].
   Future<void> deleteDraft(int id);
+
+  /// Syncs local drafts with the server IMAP Drafts folder for [accountId].
+  /// Uploads local drafts that have no [SavedDraft.imapServerId]; imports
+  /// server drafts that are not already tracked locally.
+  /// No-op when the implementation has no IMAP connection configured.
+  Future<void> syncDrafts(String accountId, String password);
 }

lib/core/services/notification_service.dart

@@ -0,0 +1,38 @@
+import 'dart:io';
+
+import 'package:flutter_local_notifications/flutter_local_notifications.dart';
+
+const _kChannelId = 'new_mail';
+const _kChannelName = 'New mail';
+
+final _plugin = FlutterLocalNotificationsPlugin();
+
+Future<void> initNotifications() async {
+  const android = AndroidInitializationSettings('@mipmap/ic_launcher');
+  await _plugin.initialize(
+    const InitializationSettings(android: android),
+    onDidReceiveNotificationResponse: (_) {},
+  );
+  await _plugin
+      .resolvePlatformSpecificImplementation<
+          AndroidFlutterLocalNotificationsPlugin>()
+      ?.requestNotificationsPermission();
+}
+
+Future<void> showNewMailNotification(String accountEmail) async {
+  if (!Platform.isAndroid) return;
+  await _plugin.show(
+    accountEmail.hashCode & 0x7FFFFFFF,
+    'New mail',
+    accountEmail,
+    const NotificationDetails(
+      android: AndroidNotificationDetails(
+        _kChannelId,
+        _kChannelName,
+        channelDescription: 'Notifications for new incoming mail',
+        importance: Importance.high,
+        priority: Priority.high,
+      ),
+    ),
+  );
+}

lib/core/sync/account_sync_manager.dart

@@ -4,6 +4,7 @@ import 'package:enough_mail/enough_mail.dart' as imap;
 import 'package:sharedinbox/core/models/account.dart';
 import 'package:sharedinbox/core/models/email.dart' show SyncEmailsResult;
 import 'package:sharedinbox/core/repositories/account_repository.dart';
+import 'package:sharedinbox/core/repositories/draft_repository.dart';
 import 'package:sharedinbox/core/repositories/email_repository.dart';
 import 'package:sharedinbox/core/repositories/mailbox_repository.dart';
 import 'package:sharedinbox/core/repositories/sync_log_repository.dart';
@@ -11,6 +12,8 @@ import 'package:sharedinbox/core/utils/logger.dart';
 import 'package:sharedinbox/data/imap/imap_client_factory.dart'
     show ImapConnectFn, connectImap, verboseLogKey;
 
+typedef OnNewMailCallback = Future<void> Function(String accountEmail);
+
 /// Manages background sync for all accounts.
 ///
 /// IMAP accounts get an IDLE-based sync loop (_AccountSync).
@@ -22,19 +25,35 @@ class AccountSyncManager {
     this._emails, {
     ImapConnectFn imapConnect = connectImap,
     SyncLogRepository syncLog = const NoOpSyncLogRepository(),
+    DraftRepository? drafts,
+    OnNewMailCallback? onNewMail,
   })  : _imapConnect = imapConnect,
-        _syncLog = syncLog;
+        _syncLog = syncLog,
+        _drafts = drafts,
+        _onNewMail = onNewMail;
 
   final AccountRepository _accounts;
   final MailboxRepository _mailboxes;
   final EmailRepository _emails;
   final ImapConnectFn _imapConnect;
   final SyncLogRepository _syncLog;
+  final DraftRepository? _drafts;
+  final OnNewMailCallback? _onNewMail;
 
   final Map<String, _SyncLoop> _active = {};
   StreamSubscription<List<Account>>? _accountsSub;
   StreamSubscription<String>? _onChangesSub;
 
+  final _syncPhaseCtrl = StreamController<(String, bool)>.broadcast();
+
+  /// Emits `true` when [accountId] starts syncing, `false` when it stops.
+  Stream<bool> watchSyncing(String accountId) =>
+      _syncPhaseCtrl.stream.where((e) => e.$1 == accountId).map((e) => e.$2);
+
+  void _emitSyncing(String accountId, {required bool syncing}) {
+    if (!_syncPhaseCtrl.isClosed) _syncPhaseCtrl.add((accountId, syncing));
+  }
+
   void start() {
     _onChangesSub = _emails.onChangesQueued.listen((accountId) {
       _active[accountId]?.kick();
@@ -45,6 +64,7 @@ class AccountSyncManager {
 
       for (final account in accounts) {
         if (_active.containsKey(account.id)) continue;
+        final id = account.id;
         final loop = switch (account.type) {
           AccountType.imap => _AccountSync(
               account,
@@ -53,6 +73,10 @@ class AccountSyncManager {
               _emails,
               _imapConnect,
               _syncLog,
+              _drafts,
+              _onNewMail,
+              onSyncStart: () => _emitSyncing(id, syncing: true),
+              onSyncEnd: () => _emitSyncing(id, syncing: false),
             ),
           AccountType.jmap => _JmapAccountSync(
               account,
@@ -60,6 +84,8 @@ class AccountSyncManager {
               _emails,
               _accounts,
               _syncLog,
+              onSyncStart: () => _emitSyncing(id, syncing: true),
+              onSyncEnd: () => _emitSyncing(id, syncing: false),
             ),
         };
         _active[account.id] = loop;
@@ -81,6 +107,7 @@ class AccountSyncManager {
       s.stop();
     }
     _active.clear();
+    unawaited(_syncPhaseCtrl.close());
   }
 
   /// Wakes the idle/wait phase of the given account's sync loop so a new
@@ -113,6 +140,10 @@ class AccountSyncManager {
           _emails,
           _imapConnect,
           _syncLog,
+          _drafts,
+          _onNewMail,
+          onSyncStart: () => _emitSyncing(accountId, syncing: true),
+          onSyncEnd: () => _emitSyncing(accountId, syncing: false),
         ),
       AccountType.jmap => _JmapAccountSync(
           account,
@@ -120,6 +151,8 @@ class AccountSyncManager {
           _emails,
           _accounts,
           _syncLog,
+          onSyncStart: () => _emitSyncing(accountId, syncing: true),
+          onSyncEnd: () => _emitSyncing(accountId, syncing: false),
         ),
     };
     _active[accountId] = loop;
@@ -145,7 +178,12 @@ class _AccountSync implements _SyncLoop {
     this._emails,
     this._imapConnect,
     this._syncLog,
-  );
+    this._drafts,
+    this._onNewMail, {
+    void Function()? onSyncStart,
+    void Function()? onSyncEnd,
+  })  : _onSyncStart = onSyncStart,
+        _onSyncEnd = onSyncEnd;
 
   final Account account;
   final AccountRepository _accounts;
@@ -153,6 +191,10 @@ class _AccountSync implements _SyncLoop {
   final EmailRepository _emails;
   final ImapConnectFn _imapConnect;
   final SyncLogRepository _syncLog;
+  final DraftRepository? _drafts;
+  final OnNewMailCallback? _onNewMail;
+  final void Function()? _onSyncStart;
+  final void Function()? _onSyncEnd;
 
   imap.ImapClient? _idleClient;
   bool _running = false;
@@ -185,6 +227,7 @@ class _AccountSync implements _SyncLoop {
   Future<void> _loop() async {
     while (_running) {
       final startedAt = DateTime.now();
+      _onSyncStart?.call();
       try {
         final (_SyncStats stats, String? capturedLog) = await _runSync(
           account.verbose,
@@ -204,8 +247,10 @@ class _AccountSync implements _SyncLoop {
           protocolLog: capturedLog,
         );
         _backoffSeconds = 5;
+        _onSyncEnd?.call();
         await _idle();
       } catch (e, st) {
+        _onSyncEnd?.call();
         final isPermanent = _isPermanentError(e);
         try {
           await _syncLog.log(
@@ -279,6 +324,8 @@ class _AccountSync implements _SyncLoop {
   Future<_SyncStats> _sync() async {
     final password = await _accounts.getPassword(account.id);
 
+    await _drafts?.syncDrafts(account.id, password);
+
     // Check for expired snoozes and move them back to Inbox before syncing.
     await _emails.wakeUpEmails(account.id);
 
@@ -325,6 +372,7 @@ class _AccountSync implements _SyncLoop {
       await client.selectMailboxByPath('INBOX');
 
       final newMessageCompleter = Completer<void>();
+      var hasNewMail = false;
 
       final sub = client.eventBus
           .on<imap.ImapEvent>()
@@ -332,7 +380,11 @@ class _AccountSync implements _SyncLoop {
             (e) =>
                 e is imap.ImapMessagesExistEvent || e is imap.ImapExpungeEvent,
           )
-          .listen((_) {
+          .listen((e) {
+        if (e is imap.ImapMessagesExistEvent &&
+            e.newMessagesExists > e.oldMessagesExists) {
+          hasNewMail = true;
+        }
         if (!newMessageCompleter.isCompleted) newMessageCompleter.complete();
       });
 
@@ -348,6 +400,10 @@ class _AccountSync implements _SyncLoop {
 
       await client.idleDone();
       await sub.cancel();
+
+      if (hasNewMail) {
+        unawaited(_onNewMail?.call(account.email));
+      }
     } finally {
       await client.logout();
       _idleClient = null;
@@ -364,14 +420,19 @@ class _JmapAccountSync implements _SyncLoop {
     this._mailboxes,
     this._emails,
     this._accounts,
-    this._syncLog,
-  );
+    this._syncLog, {
+    void Function()? onSyncStart,
+    void Function()? onSyncEnd,
+  })  : _onSyncStart = onSyncStart,
+        _onSyncEnd = onSyncEnd;
 
   final Account account;
   final MailboxRepository _mailboxes;
   final EmailRepository _emails;
   final AccountRepository _accounts;
   final SyncLogRepository _syncLog;
+  final void Function()? _onSyncStart;
+  final void Function()? _onSyncEnd;
 
   bool _running = false;
   int _backoffSeconds = 5;
@@ -403,6 +464,7 @@ class _JmapAccountSync implements _SyncLoop {
   Future<void> _loop() async {
     while (_running) {
       final startedAt = DateTime.now();
+      _onSyncStart?.call();
       try {
         final (_SyncStats stats, String? capturedLog) = await _runSync(
           account.verbose,
@@ -422,8 +484,10 @@ class _JmapAccountSync implements _SyncLoop {
           protocolLog: capturedLog,
         );
         _backoffSeconds = 5;
+        _onSyncEnd?.call();
         await _wait();
       } catch (e, st) {
+        _onSyncEnd?.call();
         final isPermanent = _isPermanentError(e);
         try {
           await _syncLog.log(

lib/core/sync/background_sync.dart

@@ -0,0 +1,123 @@
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:drift/drift.dart';
+import 'package:drift/native.dart';
+import 'package:enough_mail/enough_mail.dart' as imap;
+import 'package:path/path.dart' as p;
+import 'package:path_provider/path_provider.dart';
+
+import 'package:sharedinbox/core/models/account.dart' as model;
+import 'package:sharedinbox/core/repositories/account_repository.dart';
+import 'package:sharedinbox/core/services/notification_service.dart';
+import 'package:sharedinbox/data/db/database.dart';
+import 'package:sharedinbox/data/imap/imap_client_factory.dart';
+import 'package:sharedinbox/data/repositories/account_repository_impl.dart';
+import 'package:sharedinbox/data/storage/flutter_secure_storage_impl.dart';
+
+import 'package:workmanager/workmanager.dart';
+
+const _kTaskName = 'si_bg_sync';
+const _kResourceType = 'background_check';
+
+@pragma('vm:entry-point')
+void callbackDispatcher() {
+  Workmanager().executeTask((_, __) async {
+    try {
+      await _doBackgroundSync();
+    } catch (_) {}
+    return true;
+  });
+}
+
+Future<void> registerBackgroundSync() async {
+  await Workmanager().initialize(callbackDispatcher);
+  await Workmanager().registerPeriodicTask(
+    _kTaskName,
+    _kTaskName,
+    frequency: const Duration(minutes: 15),
+    constraints: Constraints(networkType: NetworkType.connected),
+    existingWorkPolicy: ExistingWorkPolicy.keep,
+  );
+}
+
+Future<void> _doBackgroundSync() async {
+  final dir = await getApplicationSupportDirectory();
+  final db = AppDatabase(
+    NativeDatabase(File(p.join(dir.path, 'sharedinbox.db'))),
+  );
+  try {
+    final accountRepo = AccountRepositoryImpl(
+      db,
+      const FlutterSecureStorageImpl(),
+    );
+    final accounts = await accountRepo.observeAccounts().first;
+    await initNotifications();
+    for (final account in accounts) {
+      if (account.type != model.AccountType.imap) continue;
+      await _checkAccount(db, accountRepo, account);
+    }
+  } finally {
+    await db.close();
+  }
+}
+
+Future<void> _checkAccount(
+  AppDatabase db,
+  AccountRepository accountRepo,
+  model.Account account,
+) async {
+  try {
+    final password = await accountRepo.getPassword(account.id);
+    final username =
+        account.username.isNotEmpty ? account.username : account.email;
+    final client = await connectImap(account, username, password);
+    try {
+      final status = await client.statusMailbox(
+        imap.Mailbox.virtual('INBOX', []),
+        [imap.StatusFlags.uidNext],
+      );
+      final currentUidNext = status.uidNext;
+
+      final stored = await (db.select(db.syncStates)
+            ..where(
+              (t) =>
+                  t.accountId.equals(account.id) &
+                  t.resourceType.equals(_kResourceType),
+            ))
+          .getSingleOrNull();
+      final lastUidNext = _parseUidNext(stored?.state);
+
+      await db.into(db.syncStates).insertOnConflictUpdate(
+            SyncStatesCompanion.insert(
+              accountId: account.id,
+              resourceType: _kResourceType,
+              state: jsonEncode({'uidNext': currentUidNext}),
+              syncedAt: DateTime.now(),
+            ),
+          );
+
+      if (lastUidNext != null &&
+          currentUidNext != null &&
+          currentUidNext > lastUidNext) {
+        await showNewMailNotification(account.email);
+      }
+    } finally {
+      await client.logout();
+    }
+  } catch (_) {}
+}
+
+int? _parseUidNext(String? state) {
+  if (state == null) return null;
+  try {
+    final decoded = jsonDecode(state);
+    if (decoded is Map<String, Object?>) {
+      return decoded['uidNext'] as int?;
+    }
+    return null;
+  } catch (_) {
+    return null;
+  }
+}

lib/core/utils/host_utils.dart

@@ -2,3 +2,21 @@ bool isLocalhost(String host) {
   final h = host.trim().toLowerCase();
   return h == 'localhost' || h == '127.0.0.1' || h == '::1';
 }
+
+String? validateHostname(String? value) {
+  if (value == null || value.trim().isEmpty) return 'Required';
+  return _checkHostChars(value.trim());
+}
+
+String? validateOptionalHostname(String? value) {
+  if (value == null || value.trim().isEmpty) return null;
+  return _checkHostChars(value.trim());
+}
+
+String? _checkHostChars(String h) {
+  if (h.contains(RegExp(r'[@/\\]')) ||
+      h.codeUnits.any((c) => c < 32 || c == 127)) {
+    return 'Invalid hostname';
+  }
+  return null;
+}

lib/data/db/database.dart

@@ -88,6 +88,9 @@ class Emails extends Table {
   DateTimeColumn get snoozedUntil => dateTime().nullable()();
   TextColumn get snoozedFromMailboxPath => text().nullable()();
 
+  // Added in schema v23: RFC 2369 List-Unsubscribe header value.
+  TextColumn get listUnsubscribeHeader => text().nullable()();
+
   @override
   Set<Column> get primaryKey => {id};
 }
@@ -227,6 +230,8 @@ class Drafts extends Table {
   TextColumn get subjectText => text().withDefault(const Constant(''))();
   TextColumn get bodyText => text().withDefault(const Constant(''))();
   DateTimeColumn get updatedAt => dateTime()();
+  // Added in schema v24: IMAP UID string ("mailbox:uid") on the server.
+  TextColumn get imapServerId => text().nullable()();
 }
 
 @DataClassName('UndoActionRow')
@@ -264,7 +269,7 @@ class AppDatabase extends _$AppDatabase {
   AppDatabase([QueryExecutor? executor]) : super(executor ?? _openConnection());
 
   @override
-  int get schemaVersion => 22;
+  int get schemaVersion => 24;
 
   @override
   MigrationStrategy get migration => MigrationStrategy(
@@ -420,6 +425,12 @@ class AppDatabase extends _$AppDatabase {
               ),
             );
           }
+          if (from < 23) {
+            await m.addColumn(emails, emails.listUnsubscribeHeader);
+          }
+          if (from >= 4 && from < 24) {
+            await m.addColumn(drafts, drafts.imapServerId);
+          }
         },
       );
 }

lib/data/repositories/draft_repository_impl.dart

@@ -1,13 +1,23 @@
 import 'package:drift/drift.dart';
+import 'package:enough_mail/enough_mail.dart' as imap;
 
+import 'package:sharedinbox/core/models/account.dart';
 import 'package:sharedinbox/core/models/draft.dart';
+import 'package:sharedinbox/core/repositories/account_repository.dart';
 import 'package:sharedinbox/core/repositories/draft_repository.dart';
 import 'package:sharedinbox/data/db/database.dart';
+import 'package:sharedinbox/data/imap/imap_client_factory.dart';
 
 class DraftRepositoryImpl implements DraftRepository {
-  DraftRepositoryImpl(this._db);
+  DraftRepositoryImpl(
+    this._db,
+    this._accounts, {
+    ImapConnectFn? imapConnect,
+  }) : _imapConnect = imapConnect;
 
   final AppDatabase _db;
+  final AccountRepository _accounts;
+  final ImapConnectFn? _imapConnect;
 
   @override
   Future<SavedDraft> saveDraft({
@@ -95,6 +105,110 @@ class DraftRepositoryImpl implements DraftRepository {
     await (_db.delete(_db.drafts)..where((t) => t.id.equals(id))).go();
   }
 
+  @override
+  Future<void> syncDrafts(String accountId, String password) async {
+    final connect = _imapConnect;
+    if (connect == null) return;
+
+    final account = await _accounts.getAccount(accountId);
+    if (account == null || account.type != AccountType.imap) return;
+
+    final username =
+        account.username.isNotEmpty ? account.username : account.email;
+    imap.ImapClient? client;
+    try {
+      client = await connect(account, username, password);
+      await _syncWithServer(client, accountId);
+    } finally {
+      await client?.logout();
+    }
+  }
+
+  Future<void> _syncWithServer(
+    imap.ImapClient client,
+    String accountId,
+  ) async {
+    // Create/select the Drafts folder.
+    try {
+      await client.createMailbox('Drafts');
+    } catch (_) {
+      // Already exists.
+    }
+    final selectResult = await client.selectMailboxByPath('Drafts');
+    final messageCount = selectResult.messagesExists;
+
+    // Upload local drafts that have no server counterpart.
+    final localDrafts = await (_db.select(_db.drafts)
+          ..where(
+            (t) => t.accountId.equals(accountId) & t.imapServerId.isNull(),
+          ))
+        .get();
+
+    for (final row in localDrafts) {
+      final builder = imap.MessageBuilder()
+        ..to = _parseAddresses(row.toText)
+        ..cc = _parseAddresses(row.ccText)
+        ..subject = row.subjectText
+        ..text = row.bodyText;
+      final mime = builder.buildMimeMessage();
+      final appendResult = await client.appendMessage(
+        mime,
+        targetMailboxPath: 'Drafts',
+        flags: [r'\Draft'],
+      );
+      final uidList =
+          appendResult.responseCodeAppendUid?.targetSequence.toList();
+      final uid = (uidList != null && uidList.isNotEmpty)
+          ? uidList.first.toString()
+          : null;
+      if (uid != null) {
+        await (_db.update(_db.drafts)..where((t) => t.id.equals(row.id)))
+            .write(DraftsCompanion(imapServerId: Value(uid)));
+      }
+    }
+
+    // Download server drafts not tracked locally.
+    if (messageCount > 0) {
+      final knownServerIds = await (_db.select(_db.drafts)
+            ..where(
+              (t) => t.accountId.equals(accountId) & t.imapServerId.isNotNull(),
+            ))
+          .get();
+      final knownIds = knownServerIds.map((r) => r.imapServerId!).toSet();
+
+      final seq = imap.MessageSequence.fromAll();
+      final fetch = await client.uidFetchMessages(seq, '(UID FLAGS ENVELOPE)');
+      for (final msg in fetch.messages) {
+        final uid = msg.uid?.toString();
+        if (uid == null || knownIds.contains(uid)) continue;
+        if (msg.flags?.contains(r'\Deleted') ?? false) continue;
+        final env = msg.envelope;
+        final now = DateTime.now();
+        await _db.into(_db.drafts).insert(
+              DraftsCompanion.insert(
+                accountId: Value(accountId),
+                toText: Value(_addressListToText(env?.to)),
+                ccText: Value(_addressListToText(env?.cc)),
+                subjectText: Value(env?.subject ?? ''),
+                bodyText: const Value(''),
+                updatedAt: now,
+                imapServerId: Value(uid),
+              ),
+            );
+      }
+    }
+  }
+
+  List<imap.MailAddress> _parseAddresses(String text) {
+    if (text.trim().isEmpty) return [];
+    return text.split(',').map((s) => imap.MailAddress('', s.trim())).toList();
+  }
+
+  String _addressListToText(List<imap.MailAddress>? addresses) {
+    if (addresses == null || addresses.isEmpty) return '';
+    return addresses.map((a) => a.email).join(', ');
+  }
+
   SavedDraft _toModel(Draft row) => SavedDraft(
         id: row.id,
         accountId: row.accountId,
@@ -104,5 +218,6 @@ class DraftRepositoryImpl implements DraftRepository {
         subjectText: row.subjectText,
         bodyText: row.bodyText,
         updatedAt: row.updatedAt,
+        imapServerId: row.imapServerId,
       );
 }

lib/data/repositories/email_repository_impl.dart

@@ -528,7 +528,7 @@ class EmailRepositoryImpl implements EmailRepository {
     imap.MessageSequence sequence,
   ) async {
     const fetchItems =
-        '(UID FLAGS ENVELOPE BODYSTRUCTURE RFC822.SIZE BODY.PEEK[HEADER.FIELDS (REFERENCES)])';
+        '(UID FLAGS ENVELOPE BODYSTRUCTURE RFC822.SIZE BODY.PEEK[HEADER.FIELDS (REFERENCES LIST-UNSUBSCRIBE)])';
     final fetch = sequence.isUidSequence
         ? await client.uidFetchMessages(sequence, fetchItems)
         : await client.fetchMessages(sequence, fetchItems);
@@ -569,6 +569,7 @@ class EmailRepositoryImpl implements EmailRepository {
         final msgId = envelope.messageId?.trim();
         final inReplyTo = envelope.inReplyTo?.trim();
         final refs = msg.getHeaderValue('References')?.trim();
+        final listUnsubscribe = msg.getHeaderValue('List-Unsubscribe')?.trim();
         final threadId = _computeThreadId(
               emailId: emailId,
               messageId: msgId,
@@ -612,6 +613,7 @@ class EmailRepositoryImpl implements EmailRepository {
                 inReplyTo: Value(inReplyTo),
                 references: Value(refs),
                 snoozedUntil: Value(snoozedUntil),
+                listUnsubscribeHeader: Value(listUnsubscribe),
               ),
             );
       }
@@ -950,6 +952,7 @@ class EmailRepositoryImpl implements EmailRepository {
     'htmlBody',
     'bodyValues',
     'attachments',
+    'header:List-Unsubscribe:asText',
   ];
 
   static const _emailGetBodyOptions = {
@@ -1151,6 +1154,8 @@ class EmailRepositoryImpl implements EmailRepository {
       final jmapReferences = _joinJmapStringList(
         m['references'] as List<dynamic>?,
       );
+      final jmapListUnsubscribe =
+          (m['header:List-Unsubscribe:asText'] as String?)?.trim();
 
       await _db.into(_db.emails).insertOnConflictUpdate(
             EmailsCompanion.insert(
@@ -1173,6 +1178,7 @@ class EmailRepositoryImpl implements EmailRepository {
               inReplyTo: Value(jmapInReplyTo),
               references: Value(jmapReferences),
               snoozedUntil: Value(snoozedUntil),
+              listUnsubscribeHeader: Value(jmapListUnsubscribe),
             ),
           );
 
@@ -2663,6 +2669,7 @@ class EmailRepositoryImpl implements EmailRepository {
       references: row.references,
       snoozedUntil: row.snoozedUntil,
       snoozedFromMailboxPath: row.snoozedFromMailboxPath,
+      listUnsubscribeHeader: row.listUnsubscribeHeader,
     );
   }
 

lib/di.dart

@@ -12,6 +12,7 @@ import 'package:sharedinbox/core/repositories/undo_repository.dart';
 import 'package:sharedinbox/core/services/account_discovery_service.dart';
 import 'package:sharedinbox/core/services/connection_test_service.dart';
 import 'package:sharedinbox/core/services/managesieve_probe_service.dart';
+import 'package:sharedinbox/core/services/notification_service.dart';
 import 'package:sharedinbox/core/services/undo_service.dart';
 import 'package:sharedinbox/core/storage/secure_storage.dart';
 import 'package:sharedinbox/core/sync/account_sync_manager.dart';
@@ -65,7 +66,11 @@ final mailboxRepositoryProvider = Provider<MailboxRepository>((ref) {
 });
 
 final draftRepositoryProvider = Provider<DraftRepository>((ref) {
-  return DraftRepositoryImpl(ref.watch(dbProvider));
+  return DraftRepositoryImpl(
+    ref.watch(dbProvider),
+    ref.watch(accountRepositoryProvider),
+    imapConnect: ref.watch(imapConnectProvider),
+  );
 });
 
 final emailRepositoryProvider = Provider<EmailRepository>((ref) {
@@ -110,6 +115,11 @@ final syncHealthProvider =
       .watchSingleOrNull();
 });
 
+final isSyncingProvider =
+    StreamProvider.autoDispose.family<bool, String>((ref, accountId) {
+  return ref.watch(syncManagerProvider).watchSyncing(accountId);
+});
+
 final syncManagerProvider = Provider<AccountSyncManager>((ref) {
   final manager = AccountSyncManager(
     ref.watch(accountRepositoryProvider),
@@ -117,6 +127,8 @@ final syncManagerProvider = Provider<AccountSyncManager>((ref) {
     ref.watch(emailRepositoryProvider),
     syncLog: ref.watch(syncLogRepositoryProvider),
     imapConnect: ref.watch(imapConnectProvider),
+    drafts: ref.watch(draftRepositoryProvider),
+    onNewMail: showNewMailNotification,
   );
   ref.onDispose(manager.dispose);
   return manager;

lib/main.dart

@@ -1,8 +1,11 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import 'package:sharedinbox/core/services/notification_service.dart';
+import 'package:sharedinbox/core/sync/background_sync.dart';
 import 'package:sharedinbox/data/db/database.dart';
 import 'package:sharedinbox/di.dart';
 import 'package:sharedinbox/ui/router.dart';
@@ -32,6 +35,10 @@ void main({List<Override> overrides = const []}) async {
         };
 
         await initDatabasePath();
+        if (Platform.isAndroid) {
+          await initNotifications();
+          await registerBackgroundSync();
+        }
         runApp(
           ProviderScope(overrides: overrides, child: const SharedInboxApp()),
         );

lib/ui/screens/add_account_screen.dart

@@ -408,7 +408,7 @@ class _AddAccountScreenState extends ConsumerState<AddAccountScreen> {
             _field(_passwordCtrl, 'Password', obscure: true),
             const Divider(height: 32),
             Text('IMAP', style: Theme.of(context).textTheme.titleSmall),
-            _field(_imapHostCtrl, 'Host'),
+            _field(_imapHostCtrl, 'Host', validator: validateHostname),
             _field(_imapPortCtrl, 'Port', keyboardType: TextInputType.number),
             if (isLocalhost(_imapHostCtrl.text.trim()))
               SwitchListTile(
@@ -418,7 +418,7 @@ class _AddAccountScreenState extends ConsumerState<AddAccountScreen> {
               ),
             const Divider(height: 32),
             Text('SMTP', style: Theme.of(context).textTheme.titleSmall),
-            _field(_smtpHostCtrl, 'Host'),
+            _field(_smtpHostCtrl, 'Host', validator: validateHostname),
             _field(_smtpPortCtrl, 'Port', keyboardType: TextInputType.number),
             if (isLocalhost(_smtpHostCtrl.text.trim()))
               SwitchListTile(
@@ -475,6 +475,7 @@ class _AddAccountScreenState extends ConsumerState<AddAccountScreen> {
     bool obscure = false,
     bool required = true,
     TextInputType? keyboardType,
+    String? Function(String?)? validator,
   }) {
     return Padding(
       padding: const EdgeInsets.symmetric(vertical: 6),
@@ -486,9 +487,10 @@ class _AddAccountScreenState extends ConsumerState<AddAccountScreen> {
           labelText: label,
           border: const OutlineInputBorder(),
         ),
-        validator: required
-            ? (v) => (v == null || v.trim().isEmpty) ? 'Required' : null
-            : null,
+        validator: validator ??
+            (required
+                ? (v) => (v == null || v.trim().isEmpty) ? 'Required' : null
+                : null),
       ),
     );
   }

lib/ui/screens/edit_account_screen.dart

@@ -324,11 +324,11 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
                 'IMAP (SSL/TLS)',
                 style: Theme.of(context).textTheme.titleSmall,
               ),
-              _field(_imapHostCtrl, 'Host'),
+              _field(_imapHostCtrl, 'Host', validator: validateHostname),
               _field(_imapPortCtrl, 'Port', keyboardType: TextInputType.number),
               const Divider(height: 32),
               Text('SMTP', style: Theme.of(context).textTheme.titleSmall),
-              _field(_smtpHostCtrl, 'Host'),
+              _field(_smtpHostCtrl, 'Host', validator: validateHostname),
               _field(_smtpPortCtrl, 'Port', keyboardType: TextInputType.number),
               if (isLocalhost(_smtpHostCtrl.text.trim()))
                 SwitchListTile(
@@ -348,6 +348,7 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
                     _sieveHostCtrl,
                     'Host (leave blank to use IMAP host)',
                     required: false,
+                    validator: validateOptionalHostname,
                   ),
                   _field(
                     _sievePortCtrl,
@@ -408,6 +409,7 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
     bool obscure = false,
     bool required = true,
     TextInputType? keyboardType,
+    String? Function(String?)? validator,
   }) {
     return Padding(
       padding: const EdgeInsets.symmetric(vertical: 6),
@@ -420,9 +422,10 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
           labelText: label,
           border: const OutlineInputBorder(),
         ),
-        validator: required
-            ? (v) => (v == null || v.trim().isEmpty) ? 'Required' : null
-            : null,
+        validator: validator ??
+            (required
+                ? (v) => (v == null || v.trim().isEmpty) ? 'Required' : null
+                : null),
       ),
     );
   }

lib/ui/screens/email_detail_screen.dart

@@ -13,6 +13,7 @@ import 'package:sharedinbox/core/utils/format_utils.dart';
 import 'package:sharedinbox/core/utils/html_utils.dart';
 import 'package:sharedinbox/di.dart';
 import 'package:sharedinbox/ui/widgets/snooze_picker.dart';
+import 'package:url_launcher/url_launcher.dart';
 
 final _dateFmt = DateFormat('EEE, MMM d yyyy, HH:mm');
 
@@ -267,6 +268,11 @@ class _EmailDetailScreenState extends ConsumerState<EmailDetailScreen> {
             _dateFmt.format(email.sentAt!),
             style: Theme.of(ctx).textTheme.bodySmall,
           ),
+        if (email.listUnsubscribeHeader != null)
+          Padding(
+            padding: const EdgeInsets.only(top: 8),
+            child: _UnsubscribeChip(header: email.listUnsubscribeHeader!),
+          ),
       ],
     );
   }
@@ -462,6 +468,39 @@ class _EmailDetailScreenState extends ConsumerState<EmailDetailScreen> {
   }
 }
 
+/// Parses a List-Unsubscribe header and returns the first usable URI.
+/// Prefers mailto: so unsubscribing sends an email; falls back to https:.
+Uri? _parseUnsubscribeUri(String header) {
+  final matches = RegExp(r'<([^>]+)>').allMatches(header);
+  Uri? fallback;
+  for (final m in matches) {
+    final raw = m.group(1)!.trim();
+    final uri = Uri.tryParse(raw);
+    if (uri == null) continue;
+    if (uri.scheme == 'mailto') return uri;
+    if ((uri.scheme == 'https' || uri.scheme == 'http') && fallback == null) {
+      fallback = uri;
+    }
+  }
+  return fallback;
+}
+
+class _UnsubscribeChip extends StatelessWidget {
+  const _UnsubscribeChip({required this.header});
+  final String header;
+
+  @override
+  Widget build(BuildContext context) {
+    final uri = _parseUnsubscribeUri(header);
+    if (uri == null) return const SizedBox.shrink();
+    return ActionChip(
+      avatar: const Icon(Icons.unsubscribe_outlined, size: 16),
+      label: const Text('Unsubscribe'),
+      onPressed: () => launchUrl(uri, mode: LaunchMode.externalApplication),
+    );
+  }
+}
+
 class _BlockRemoteImagesExtension extends HtmlExtension {
   @override
   Set<String> get supportedTags => {'img'};

lib/ui/screens/email_list_screen.dart

@@ -180,22 +180,7 @@ class _EmailListScreenState extends ConsumerState<EmailListScreen> {
                   ),
                 ),
               ),
-              IconButton(
-                icon: const Icon(Icons.sync),
-                onPressed: () async {
-                  try {
-                    await emailRepo.syncEmails(
-                      widget.accountId,
-                      widget.mailboxPath,
-                    );
-                  } catch (e) {
-                    if (!mounted) return;
-                    ScaffoldMessenger.of(
-                      context,
-                    ).showSnackBar(SnackBar(content: Text('Sync failed: $e')));
-                  }
-                },
-              ),
+              _buildSyncButton(emailRepo),
               IconButton(
                 icon: const Icon(Icons.edit),
                 onPressed: () => context.push(
@@ -229,6 +214,44 @@ class _EmailListScreenState extends ConsumerState<EmailListScreen> {
     );
   }
 
+  Widget _buildSyncButton(EmailRepository emailRepo) {
+    final isSyncing =
+        ref.watch(isSyncingProvider(widget.accountId)).valueOrNull ?? false;
+    final hasError =
+        ref.watch(syncLastErrorProvider(widget.accountId)).valueOrNull != null;
+    return IconButton(
+      tooltip: isSyncing
+          ? 'Syncing…'
+          : hasError
+              ? 'Sync error'
+              : 'Sync',
+      icon: isSyncing
+          ? const SizedBox(
+              width: 20,
+              height: 20,
+              child: CircularProgressIndicator(strokeWidth: 2),
+            )
+          : hasError
+              ? const Icon(Icons.sync_problem, color: Colors.red)
+              : const Icon(Icons.sync),
+      onPressed: isSyncing
+          ? null
+          : () async {
+              try {
+                await emailRepo.syncEmails(
+                  widget.accountId,
+                  widget.mailboxPath,
+                );
+              } catch (e) {
+                if (!mounted) return;
+                ScaffoldMessenger.of(context).showSnackBar(
+                  SnackBar(content: Text('Sync failed: $e')),
+                );
+              }
+            },
+    );
+  }
+
   Widget _selectionBottomBar() {
     return BottomAppBar(
       child: Row(

pubspec.yaml

@@ -45,6 +45,10 @@ dependencies:
   url_launcher: ^6.3.2
   flutter_markdown: ^0.7.7+1
 
+  # Background sync and local notifications
+  flutter_local_notifications: ^18.0.1
+  workmanager: ^0.5.2
+
 dev_dependencies:
   flutter_test:
     sdk: flutter

scripts/check_coverage.dart

@@ -52,6 +52,7 @@ const _excluded = {
   'lib/ui/widgets/try_connection_button.dart',
   'lib/ui/widgets/undo_shell.dart',
   'lib/core/sync/account_sync_manager.dart',
+  'lib/core/sync/background_sync.dart',
   'lib/core/sync/reliability_runner.dart',
   'lib/data/jmap/jmap_client.dart',
   'lib/data/jmap/sieve_repository.dart',

test/unit/account_sync_manager_test.mocks.dart

@@ -187,6 +187,16 @@ class MockMailboxRepository extends _i1.Mock implements _i7.MailboxRepository {
         ),
         returnValue: _i4.Future<_i8.Mailbox?>.value(),
       ) as _i4.Future<_i8.Mailbox?>);
+
+  @override
+  _i4.Future<void> clearForResync(String? accountId) => (super.noSuchMethod(
+        Invocation.method(
+          #clearForResync,
+          [accountId],
+        ),
+        returnValue: _i4.Future<void>.value(),
+        returnValueForMissingStub: _i4.Future<void>.value(),
+      ) as _i4.Future<void>);
 }
 
 /// A class which mocks [EmailRepository].
@@ -582,4 +592,14 @@ class MockEmailRepository extends _i1.Mock implements _i9.EmailRepository {
           ),
         )),
       ) as _i4.Future<_i2.ReliabilityResult>);
+
+  @override
+  _i4.Future<void> clearForResync(String? accountId) => (super.noSuchMethod(
+        Invocation.method(
+          #clearForResync,
+          [accountId],
+        ),
+        returnValue: _i4.Future<void>.value(),
+        returnValueForMissingStub: _i4.Future<void>.value(),
+      ) as _i4.Future<void>);
 }

test/unit/draft_repository_impl_test.dart

@@ -1,9 +1,25 @@
 import 'package:flutter_test/flutter_test.dart';
-
+import 'package:sharedinbox/core/models/account.dart';
+import 'package:sharedinbox/core/repositories/account_repository.dart';
 import 'package:sharedinbox/data/repositories/draft_repository_impl.dart';
 
 import 'db_test_helper.dart';
 
+class _StubAccounts implements AccountRepository {
+  @override
+  Stream<List<Account>> observeAccounts() => const Stream.empty();
+  @override
+  Future<Account?> getAccount(String id) async => null;
+  @override
+  Future<void> addAccount(Account account, String password) async {}
+  @override
+  Future<void> updateAccount(Account account, {String? password}) async {}
+  @override
+  Future<void> removeAccount(String id) async {}
+  @override
+  Future<String> getPassword(String accountId) async => '';
+}
+
 void main() {
   setUpAll(configureSqliteForTests);
 
@@ -11,7 +27,7 @@ void main() {
     test(
       'saveDraft creates a new row and returns it with a non-zero id',
       () async {
-        final repo = DraftRepositoryImpl(openTestDatabase());
+        final repo = DraftRepositoryImpl(openTestDatabase(), _StubAccounts());
         final draft = await repo.saveDraft(
           toText: 'bob@example.com',
           ccText: '',
@@ -25,7 +41,7 @@ void main() {
     );
 
     test('saveDraft with id updates existing row', () async {
-      final repo = DraftRepositoryImpl(openTestDatabase());
+      final repo = DraftRepositoryImpl(openTestDatabase(), _StubAccounts());
       final created = await repo.saveDraft(
         toText: 'a@example.com',
         ccText: '',
@@ -47,19 +63,19 @@ void main() {
     });
 
     test('getDraft returns null for unknown id', () async {
-      final repo = DraftRepositoryImpl(openTestDatabase());
+      final repo = DraftRepositoryImpl(openTestDatabase(), _StubAccounts());
       expect(await repo.getDraft(99999), isNull);
     });
 
     test('findDraft returns null when no draft exists', () async {
-      final repo = DraftRepositoryImpl(openTestDatabase());
+      final repo = DraftRepositoryImpl(openTestDatabase(), _StubAccounts());
       expect(await repo.findDraft(), isNull);
     });
 
     test(
       'findDraft returns most recent draft for matching replyToEmailId',
       () async {
-        final repo = DraftRepositoryImpl(openTestDatabase());
+        final repo = DraftRepositoryImpl(openTestDatabase(), _StubAccounts());
         await repo.saveDraft(
           replyToEmailId: 'email-1',
           toText: 'a@example.com',
@@ -83,7 +99,7 @@ void main() {
     test(
       'findDraft with null replyToEmailId finds new-message drafts',
       () async {
-        final repo = DraftRepositoryImpl(openTestDatabase());
+        final repo = DraftRepositoryImpl(openTestDatabase(), _StubAccounts());
         // This draft is a reply and should NOT be returned.
         await repo.saveDraft(
           replyToEmailId: 'email-1',
@@ -104,7 +120,7 @@ void main() {
     );
 
     test('deleteDraft removes the row', () async {
-      final repo = DraftRepositoryImpl(openTestDatabase());
+      final repo = DraftRepositoryImpl(openTestDatabase(), _StubAccounts());
       final draft = await repo.saveDraft(
         toText: 'a@example.com',
         ccText: '',

test/unit/email_repository_impl_test.dart

@@ -1,7 +1,7 @@
 import 'dart:async';
 import 'dart:convert';
 
-import 'package:drift/drift.dart' show Value;
+import 'package:drift/drift.dart' hide isNull, isNotNull;
 import 'package:enough_mail/enough_mail.dart' as imap;
 import 'package:flutter_test/flutter_test.dart';
 import 'package:http/http.dart' as http;
@@ -16,6 +16,7 @@ import 'package:sharedinbox/data/repositories/email_repository_impl.dart';
 
 import 'account_repository_impl_test.dart' show MapSecureStorage;
 import 'db_test_helper.dart';
+import 'fake_imap.dart' show FakeImapClient;
 // ── Helpers ───────────────────────────────────────────────────────────────────
 
 const _account = Account(
@@ -162,15 +163,19 @@ Future<imap.SmtpClient> _noSmtpConnect(Account a, String u, String p) =>
     Future.error(UnsupportedError('SMTP unavailable in unit tests'));
 
 ({AppDatabase db, AccountRepositoryImpl accounts, EmailRepositoryImpl emails})
-    _makeRepos({http.Client? httpClient}) {
+    _makeRepos({
+  http.Client? httpClient,
+  Future<imap.ImapClient> Function(Account, String, String)? imapConnect,
+  Future<imap.SmtpClient> Function(Account, String, String)? smtpConnect,
+}) {
   final db = openTestDatabase();
   final storage = MapSecureStorage();
   final accounts = AccountRepositoryImpl(db, storage);
   final emails = EmailRepositoryImpl(
     db,
     accounts,
-    imapConnect: _noImapConnect,
-    smtpConnect: _noSmtpConnect,
+    imapConnect: imapConnect ?? _noImapConnect,
+    smtpConnect: smtpConnect ?? _noSmtpConnect,
     httpClient: httpClient,
   );
   return (db: db, accounts: accounts, emails: emails);
@@ -1935,6 +1940,163 @@ void main() {
       expect(row.lastError, isNull);
     });
   });
+
+  group('concurrent moves', () {
+    test(
+        'two simultaneous moves enqueue two changes and leave email in last destination',
+        () async {
+      final r = _makeRepos();
+      await r.accounts.addAccount(_account, 'pw');
+      await r.db.into(r.db.emails).insert(
+            EmailsCompanion.insert(
+              id: 'acc-1:5',
+              accountId: 'acc-1',
+              mailboxPath: 'INBOX',
+              uid: 5,
+              receivedAt: DateTime(2024),
+            ),
+          );
+
+      // Fire both moves without awaiting to exercise concurrent enqueue logic.
+      final f1 = r.emails.moveEmail('acc-1:5', 'Archive');
+      final f2 = r.emails.moveEmail('acc-1:5', 'Trash');
+      await Future.wait([f1, f2]);
+
+      final changes = await r.db.select(r.db.pendingChanges).get();
+      expect(changes, hasLength(2));
+      expect(changes.map((c) => c.changeType), everyElement('move'));
+
+      final destinations =
+          changes.map((c) => (jsonDecode(c.payload) as Map)['dest']).toSet();
+      expect(destinations, containsAll(['Archive', 'Trash']));
+
+      final email = await r.emails.getEmail('acc-1:5');
+      expect(
+        email!.mailboxPath,
+        anyOf('Archive', 'Trash'),
+        reason:
+            'email must be optimistically moved to one of the two destinations',
+      );
+    });
+  });
+
+  group('IMAP SMTP auth failure', () {
+    test('sendEmail propagates SMTP authentication error', () async {
+      final r = _makeRepos(
+        smtpConnect: (Account _, String __, String ___) => Future.error(
+          Exception('535 5.7.8 Authentication credentials invalid'),
+        ),
+      );
+      await r.accounts.addAccount(_account, 'pw');
+
+      const draft = EmailDraft(
+        from: EmailAddress(name: 'Alice', email: 'alice@example.com'),
+        to: [EmailAddress(name: 'Bob', email: 'bob@example.com')],
+        cc: [],
+        subject: 'Test',
+        body: 'Body',
+      );
+
+      await expectLater(
+        r.emails.sendEmail('acc-1', draft),
+        throwsA(
+          isA<Exception>().having(
+            (e) => e.toString(),
+            'message',
+            contains('535'),
+          ),
+        ),
+      );
+    });
+  });
+
+  group('IMAP UID validity change', () {
+    test('full re-sync wipes stale emails when uidValidity changes', () async {
+      final r = _makeRepos(
+        imapConnect: (Account _, String __, String ___) async =>
+            _FakeImapClientUidValidity(456),
+      );
+      await r.accounts.addAccount(_account, 'pw');
+
+      // Pre-seed two emails from the old server epoch (uidValidity=123).
+      await r.db.into(r.db.emails).insert(
+            EmailsCompanion.insert(
+              id: 'acc-1:1',
+              accountId: 'acc-1',
+              mailboxPath: 'INBOX',
+              uid: 1,
+              receivedAt: DateTime(2024),
+            ),
+          );
+      await r.db.into(r.db.emails).insert(
+            EmailsCompanion.insert(
+              id: 'acc-1:2',
+              accountId: 'acc-1',
+              mailboxPath: 'INBOX',
+              uid: 2,
+              receivedAt: DateTime(2024),
+            ),
+          );
+
+      // Seed an IMAP checkpoint with the old uidValidity so the code detects
+      // a mismatch and triggers a full re-sync.
+      await r.db.into(r.db.syncStates).insertOnConflictUpdate(
+            SyncStatesCompanion.insert(
+              accountId: 'acc-1',
+              resourceType: 'IMAP:INBOX',
+              state: '{"uidValidity":123,"lastUid":2,"highestModSeq":null}',
+              syncedAt: DateTime(2024),
+            ),
+          );
+
+      await r.emails.syncEmails('acc-1', 'INBOX');
+
+      // Old emails must be wiped; the fake server returns zero messages.
+      final remaining = await r.db.select(r.db.emails).get();
+      expect(remaining, isEmpty);
+
+      // Checkpoint must be updated to the new uidValidity.
+      final stateRow = await (r.db.select(r.db.syncStates)
+            ..where(
+              (t) =>
+                  t.accountId.equals('acc-1') &
+                  t.resourceType.equals('IMAP:INBOX'),
+            ))
+          .getSingleOrNull();
+      expect(stateRow, isNotNull);
+      final state = jsonDecode(stateRow!.state) as Map<String, dynamic>;
+      expect(state['uidValidity'], 456);
+    });
+  });
+}
+
+// ── Additional fake IMAP client for UID-validity tests ───────────────────────
+
+class _FakeImapClientUidValidity extends FakeImapClient {
+  _FakeImapClientUidValidity(this._uidValidity);
+  final int _uidValidity;
+
+  @override
+  Future<imap.Mailbox> selectMailboxByPath(
+    String path, {
+    bool enableCondStore = false,
+    imap.QResyncParameters? qresync,
+  }) async =>
+      imap.Mailbox(
+        encodedName: path,
+        encodedPath: path,
+        flags: [],
+        pathSeparator: '/',
+        uidValidity: _uidValidity,
+      );
+
+  @override
+  Future<imap.SearchImapResult> uidSearchMessages({
+    String searchCriteria = 'ALL',
+    List<imap.ReturnOption>? returnOptions,
+    Duration? responseTimeout,
+  }) async =>
+      imap.SearchImapResult();
 }
 
 // ── SSE test helper ──────────────────────────────────────────────────────────

test/unit/reliability_runner_test.dart

@@ -0,0 +1,348 @@
+import 'dart:async';
+import 'package:fake_async/fake_async.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:sharedinbox/core/models/account.dart';
+import 'package:sharedinbox/core/models/email.dart';
+import 'package:sharedinbox/core/models/mailbox.dart';
+import 'package:sharedinbox/core/repositories/account_repository.dart';
+import 'package:sharedinbox/core/repositories/email_repository.dart';
+import 'package:sharedinbox/core/repositories/mailbox_repository.dart';
+import 'package:sharedinbox/core/repositories/sync_log_repository.dart';
+import 'package:sharedinbox/core/sync/account_sync_manager.dart';
+
+// ── helpers ───────────────────────────────────────────────────────────────────
+
+Account _account({String id = 'a1'}) => Account(
+      id: id,
+      displayName: 'Test',
+      email: 'test@example.com',
+      imapHost: 'localhost',
+    );
+
+class _FakeAccounts implements AccountRepository {
+  final List<Account> accounts;
+  _FakeAccounts([Account? account]) : accounts = [account ?? _account()];
+
+  @override
+  Stream<List<Account>> observeAccounts() => Stream.value(accounts);
+  @override
+  Future<Account?> getAccount(String id) async =>
+      accounts.cast<Account?>().firstWhere(
+            (a) => a?.id == id,
+            orElse: () => null,
+          );
+  @override
+  Future<void> addAccount(Account account, String password) async {}
+  @override
+  Future<void> updateAccount(Account account, {String? password}) async {}
+  @override
+  Future<void> removeAccount(String id) async {}
+  @override
+  Future<String> getPassword(String id) async => 'secret';
+}
+
+class _FakeMailboxes implements MailboxRepository {
+  final List<Mailbox> mailboxes;
+  _FakeMailboxes([this.mailboxes = const []]);
+  @override
+  Stream<List<Mailbox>> observeMailboxes(String? accountId) =>
+      Stream.value(mailboxes);
+  @override
+  Future<int> syncMailboxes(String accountId) async => 0;
+  @override
+  Future<Mailbox?> findMailboxByRole(String accountId, String role) async =>
+      null;
+  @override
+  Future<void> clearForResync(String accountId) async {}
+}
+
+class _CountingEmails implements EmailRepository {
+  int syncCount = 0;
+  int wakeUpCount = 0;
+  final Exception? syncError;
+
+  _CountingEmails({this.syncError});
+
+  @override
+  Future<SyncEmailsResult> syncEmails(String accountId, String mailbox) async {
+    syncCount++;
+    if (syncError != null) throw syncError!;
+    return SyncEmailsResult.zero;
+  }
+
+  @override
+  Future<int> wakeUpEmails(String accountId) async {
+    wakeUpCount++;
+    return 0;
+  }
+
+  @override
+  Future<int> flushPendingChanges(String accountId, String password) async => 0;
+  @override
+  Stream<List<Email>> observeEmails(String a, String m) => Stream.value([]);
+  @override
+  Stream<List<EmailThread>> observeThreads(String a, String m) =>
+      Stream.value([]);
+  @override
+  Stream<List<Email>> observeEmailsInThread(String a, String m, String t) =>
+      Stream.value([]);
+  @override
+  Future<Email?> getEmail(String id) async => null;
+  @override
+  Future<EmailBody> getEmailBody(String id) async =>
+      const EmailBody(emailId: '', attachments: []);
+  @override
+  Future<void> setFlag(String id, {bool? seen, bool? flagged}) async {}
+  @override
+  Future<void> moveEmail(String id, String dest) async {}
+  @override
+  Future<String?> deleteEmail(String id) async => null;
+  @override
+  Future<void> sendEmail(String accountId, EmailDraft draft) async {}
+  @override
+  Future<String> downloadAttachment(String id, EmailAttachment att) async => '';
+  @override
+  Future<List<Email>> searchEmails(String a, String m, String q) async => [];
+  @override
+  Future<List<Email>> searchEmailsGlobal(String? a, String q) async => [];
+  @override
+  Future<List<Email>> getEmailsByAddress(String? a, String addr) async => [];
+  @override
+  Stream<List<FailedMutation>> observeFailedMutations(String a) =>
+      Stream.value([]);
+  @override
+  Future<void> discardMutation(int id) async {}
+  @override
+  Future<void> retryMutation(int id) async {}
+  @override
+  Future<bool> cancelPendingChange(String id, String type) async => false;
+  @override
+  Future<void> snoozeEmail(String id, DateTime until) async {}
+  @override
+  Future<void> restoreEmails(List<Email> emails) async {}
+  @override
+  Stream<String> get onChangesQueued => const Stream.empty();
+  @override
+  Stream<void> watchJmapPush(String accountId, String password) =>
+      const Stream.empty();
+  @override
+  Future<ReliabilityResult> verifySyncReliability(
+    String accountId,
+    String mailboxPath,
+  ) async =>
+      ReliabilityResult.healthy;
+  @override
+  Future<void> clearForResync(String accountId) async {}
+}
+
+class _FakeSyncLog implements SyncLogRepository {
+  final logs = <bool>[];
+  @override
+  Future<void> log({
+    required String accountId,
+    required bool success,
+    String? errorMessage,
+    required String protocol,
+    required int emailsFetched,
+    required int emailsSkipped,
+    required int mailboxesSynced,
+    required int pendingFlushed,
+    required int bytesTransferred,
+    required DateTime startedAt,
+    required DateTime finishedAt,
+    List<MailboxSyncStats> mailboxStats = const [],
+    String? protocolLog,
+  }) async {
+    logs.add(success);
+  }
+
+  @override
+  Stream<List<SyncLogEntry>> observeSyncLogs(String accountId) =>
+      Stream.value([]);
+
+  @override
+  Stream<String?> observeLastError(String accountId) => Stream.value(null);
+}
+
+// ── tests ─────────────────────────────────────────────────────────────────────
+
+void main() {
+  group('AccountSyncManager backoff', () {
+    test('backoff is capped at 900 s after repeated failures', () {
+      fakeAsync((async) {
+        final emails = _CountingEmails(
+          syncError: Exception('connection refused'),
+        );
+        final syncLog = _FakeSyncLog();
+        final manager = AccountSyncManager(
+          _FakeAccounts(),
+          _FakeMailboxes([
+            const Mailbox(
+              id: 'INBOX',
+              accountId: 'a1',
+              path: 'INBOX',
+              name: 'Inbox',
+              unreadCount: 0,
+              totalCount: 0,
+            ),
+          ]),
+          emails,
+          syncLog: syncLog,
+          imapConnect: (_, __, ___) async =>
+              throw Exception('connection refused'),
+        );
+
+        manager.start();
+
+        // Advance 3 hours — long enough to observe many retries.
+        // With max backoff 900 s, we expect at least floor(3*3600/900) = 12
+        // attempts, and at most 3*3600/5 = 2160 (if backoff never grew).
+        async.elapse(const Duration(hours: 3));
+
+        final failCount = syncLog.logs.where((ok) => !ok).length;
+        expect(
+          failCount,
+          greaterThan(10),
+          reason: 'should have retried many times within 3 h',
+        );
+        expect(
+          failCount,
+          lessThan(2200),
+          reason: 'backoff must have kicked in — not every 5 s for 3 h',
+        );
+
+        manager.dispose();
+        async.elapse(const Duration(seconds: 1));
+      });
+    });
+
+    test('backoff resets to 5 s after a successful sync', () {
+      fakeAsync((async) {
+        int callCount = 0;
+        final syncLog = _FakeSyncLog();
+
+        var failsLeft = 5;
+        final customEmails = _OverrideEmails(
+          onSync: (_) async {
+            callCount++;
+            if (failsLeft > 0) {
+              failsLeft--;
+              throw Exception('transient error');
+            }
+            return SyncEmailsResult.zero;
+          },
+        );
+
+        final manager = AccountSyncManager(
+          _FakeAccounts(),
+          _FakeMailboxes([
+            const Mailbox(
+              id: 'INBOX',
+              accountId: 'a1',
+              path: 'INBOX',
+              name: 'Inbox',
+              unreadCount: 0,
+              totalCount: 0,
+            ),
+          ]),
+          customEmails,
+          syncLog: syncLog,
+          imapConnect: (_, __, ___) async =>
+              throw Exception('skip idle — force immediate loop'),
+        );
+
+        manager.start();
+
+        // Allow errors + backoff to build up, then a success, then more loops.
+        async.elapse(const Duration(seconds: 3600));
+
+        // After success, backoff should reset; failures before success should
+        // be exactly 5, and subsequent loops should fire frequently.
+        final successCount = syncLog.logs.where((ok) => ok).length;
+        expect(
+          successCount,
+          greaterThan(0),
+          reason: 'should have at least one success',
+        );
+        expect(
+          callCount,
+          greaterThan(5),
+          reason: 'should retry after failures and continue after success',
+        );
+
+        manager.dispose();
+        async.elapse(const Duration(seconds: 1));
+      });
+    });
+
+    test('concurrent sync errors from multiple accounts stay bounded', () {
+      fakeAsync((async) {
+        final accounts = _FakeAccounts()
+          ..accounts.add(_account(id: 'a2'))
+          ..accounts.add(_account(id: 'a3'));
+        final syncLog = _FakeSyncLog();
+        final manager = AccountSyncManager(
+          accounts,
+          _FakeMailboxes([
+            const Mailbox(
+              id: 'INBOX',
+              accountId: 'a1',
+              path: 'INBOX',
+              name: 'Inbox',
+              unreadCount: 0,
+              totalCount: 0,
+            ),
+            const Mailbox(
+              id: 'INBOX',
+              accountId: 'a2',
+              path: 'INBOX',
+              name: 'Inbox',
+              unreadCount: 0,
+              totalCount: 0,
+            ),
+            const Mailbox(
+              id: 'INBOX',
+              accountId: 'a3',
+              path: 'INBOX',
+              name: 'Inbox',
+              unreadCount: 0,
+              totalCount: 0,
+            ),
+          ]),
+          _CountingEmails(syncError: Exception('network error')),
+          syncLog: syncLog,
+          imapConnect: (_, __, ___) async =>
+              throw Exception('connection refused'),
+        );
+
+        manager.start();
+        async.elapse(const Duration(hours: 2));
+
+        // All 3 accounts retry, each bounded by the 900 s cap.
+        final failCount = syncLog.logs.where((ok) => !ok).length;
+        expect(failCount, greaterThan(5));
+        expect(
+          failCount,
+          lessThan(5000),
+          reason: 'backoff must be in effect across all accounts',
+        );
+
+        manager.dispose();
+        async.elapse(const Duration(seconds: 1));
+      });
+    });
+  });
+}
+
+// ── _OverrideEmails ───────────────────────────────────────────────────────────
+
+class _OverrideEmails extends _CountingEmails {
+  _OverrideEmails({required Future<SyncEmailsResult> Function(String) onSync})
+      : _onSync = onSync;
+
+  final Future<SyncEmailsResult> Function(String) _onSync;
+
+  @override
+  Future<SyncEmailsResult> syncEmails(String accountId, String mailbox) =>
+      _onSync(mailbox);
+}

test/unit/undo_service_test.mocks.dart

@@ -452,6 +452,16 @@ class MockEmailRepository extends _i1.Mock implements _i3.EmailRepository {
           ),
         )),
       ) as _i4.Future<_i2.ReliabilityResult>);
+
+  @override
+  _i4.Future<void> clearForResync(String? accountId) => (super.noSuchMethod(
+        Invocation.method(
+          #clearForResync,
+          [accountId],
+        ),
+        returnValue: _i4.Future<void>.value(),
+        returnValueForMissingStub: _i4.Future<void>.value(),
+      ) as _i4.Future<void>);
 }
 
 /// A class which mocks [UndoRepository].

test/widget/helpers.dart

@@ -114,6 +114,9 @@ class FakeDraftRepository implements DraftRepository {
 
   @override
   Future<void> deleteDraft(int id) async => _drafts.remove(id);
+
+  @override
+  Future<void> syncDrafts(String accountId, String password) async {}
 }
 
 class FakeMailboxRepository implements MailboxRepository {