diff --git a/lib/core/models/account.dart b/lib/core/models/account.dart
index 73e8d65..9c69e79 100644
--- a/lib/core/models/account.dart
+++ b/lib/core/models/account.dart
@@ -21,6 +21,11 @@ class Account {
   /// then to the local part of [email] (the part before '@').
   final String username;
 
+  /// When true, raw protocol traffic is captured and written to the sync log.
+  /// Never enable in production — logs contain sensitive data even after
+  /// credential redaction.
+  final bool verbose;
+
   const Account({
     required this.id,
     required this.displayName,
@@ -34,5 +39,6 @@ class Account {
     this.smtpPort = 587,
     this.smtpSsl = false,
     this.jmapUrl,
+    this.verbose = false,
   });
 }
diff --git a/lib/core/repositories/sync_log_repository.dart b/lib/core/repositories/sync_log_repository.dart
index d1c47c7..15efd4a 100644
--- a/lib/core/repositories/sync_log_repository.dart
+++ b/lib/core/repositories/sync_log_repository.dart
@@ -26,6 +26,7 @@ class SyncLogEntry {
     required this.startedAt,
     required this.finishedAt,
     this.mailboxStats = const [],
+    this.protocolLog,
   });
 
   final int id;
@@ -40,6 +41,7 @@ class SyncLogEntry {
   final DateTime startedAt;
   final DateTime finishedAt;
   final List<MailboxSyncStats> mailboxStats;
+  final String? protocolLog;
 
   Duration get duration => finishedAt.difference(startedAt);
   bool get isOk => result == 'ok';
@@ -59,6 +61,7 @@ abstract class SyncLogRepository {
     required DateTime startedAt,
     required DateTime finishedAt,
     List<MailboxSyncStats> mailboxStats = const [],
+    String? protocolLog,
   });
 
   Stream<List<SyncLogEntry>> observeSyncLogs(String accountId);
@@ -81,6 +84,7 @@ class NoOpSyncLogRepository implements SyncLogRepository {
     required DateTime startedAt,
     required DateTime finishedAt,
     List<MailboxSyncStats> mailboxStats = const [],
+    String? protocolLog,
   }) async {}
 
   @override
diff --git a/lib/core/sync/account_sync_manager.dart b/lib/core/sync/account_sync_manager.dart
index f41bce0..43f10fb 100644
--- a/lib/core/sync/account_sync_manager.dart
+++ b/lib/core/sync/account_sync_manager.dart
@@ -2,7 +2,8 @@ import 'dart:async';
 
 import 'package:enough_mail/enough_mail.dart' as imap;
 
-import '../../data/imap/imap_client_factory.dart';
+import '../../data/imap/imap_client_factory.dart'
+    show ImapConnectFn, connectImap, verboseLogKey;
 import '../models/account.dart';
 import '../models/email.dart' show SyncEmailsResult;
 import '../repositories/account_repository.dart';
@@ -124,7 +125,8 @@ class _AccountSync implements _SyncLoop {
     while (_running) {
       final startedAt = DateTime.now();
       try {
-        final stats = await _sync();
+        final (_SyncStats stats, String? capturedLog) =
+            await _runSync(account.verbose);
         await _syncLog.log(
           accountId: account.id,
           success: true,
@@ -137,6 +139,7 @@ class _AccountSync implements _SyncLoop {
           startedAt: startedAt,
           finishedAt: DateTime.now(),
           mailboxStats: stats.mailboxStats,
+          protocolLog: capturedLog,
         );
         await _idle();
         _backoffSeconds = 5;
@@ -169,6 +172,19 @@ class _AccountSync implements _SyncLoop {
     }
   }
 
+  Future<(_SyncStats, String?)> _runSync(bool verbose) async {
+    if (!verbose) return (await _sync(), null);
+    final buffer = StringBuffer();
+    final stats = await runZoned(
+      _sync,
+      zoneValues: {verboseLogKey: buffer},
+      zoneSpecification: ZoneSpecification(
+        print: (_, __, ___, line) => buffer.writeln(line),
+      ),
+    );
+    return (stats, _redactCredentials(buffer.toString()));
+  }
+
   Future<_SyncStats> _sync() async {
     final password = await _accounts.getPassword(account.id);
     final pendingFlushed =
@@ -284,7 +300,8 @@ class _JmapAccountSync implements _SyncLoop {
     while (_running) {
       final startedAt = DateTime.now();
       try {
-        final stats = await _sync();
+        final (_SyncStats stats, String? capturedLog) =
+            await _runSync(account.verbose);
         await _syncLog.log(
           accountId: account.id,
           success: true,
@@ -297,6 +314,7 @@ class _JmapAccountSync implements _SyncLoop {
           startedAt: startedAt,
           finishedAt: DateTime.now(),
           mailboxStats: stats.mailboxStats,
+          protocolLog: capturedLog,
         );
         _backoffSeconds = 5;
         await _wait();
@@ -329,6 +347,19 @@ class _JmapAccountSync implements _SyncLoop {
     }
   }
 
+  Future<(_SyncStats, String?)> _runSync(bool verbose) async {
+    if (!verbose) return (await _sync(), null);
+    final buffer = StringBuffer();
+    final stats = await runZoned(
+      _sync,
+      zoneValues: {verboseLogKey: buffer},
+      zoneSpecification: ZoneSpecification(
+        print: (_, __, ___, line) => buffer.writeln(line),
+      ),
+    );
+    return (stats, buffer.toString());
+  }
+
   Future<_SyncStats> _sync() async {
     final password = await _accounts.getPassword(account.id);
 
@@ -418,3 +449,19 @@ class _SyncStats {
   final int bytesTransferred;
   final List<MailboxSyncStats> mailboxStats;
 }
+
+/// Replaces credentials in a captured IMAP protocol log.
+///
+/// Redacts the password argument from LOGIN commands and the base64 payload
+/// from AUTHENTICATE commands. Other lines pass through unchanged.
+String _redactCredentials(String log) {
+  return log
+      .replaceAllMapped(
+        RegExp(r'(LOGIN\s+\S+\s+)\S+', caseSensitive: false),
+        (m) => '${m.group(1)}[REDACTED]',
+      )
+      .replaceAllMapped(
+        RegExp(r'(AUTHENTICATE\s+\w+\s+)\S+', caseSensitive: false),
+        (m) => '${m.group(1)}[REDACTED]',
+      );
+}
diff --git a/lib/data/db/database.dart b/lib/data/db/database.dart
index f146615..324b121 100644
--- a/lib/data/db/database.dart
+++ b/lib/data/db/database.dart
@@ -24,6 +24,8 @@ class Accounts extends Table {
   TextColumn get jmapUrl => text().nullable()();
   // Added in schema v3:
   TextColumn get username => text().withDefault(const Constant(''))();
+  // Added in schema v13:
+  BoolColumn get verbose => boolean().withDefault(const Constant(false))();
 
   @override
   Set<Column> get primaryKey => {id};
@@ -137,6 +139,8 @@ class SyncLogs extends Table {
   IntColumn get bytesTransferred => integer().withDefault(const Constant(0))();
   DateTimeColumn get startedAt => dateTime()();
   DateTimeColumn get finishedAt => dateTime()();
+  // Added in schema v13: raw protocol log when account.verbose == true.
+  TextColumn get protocolLog => text().nullable()();
 }
 
 /// Per-mailbox breakdown for a single sync cycle.
@@ -185,7 +189,7 @@ class AppDatabase extends _$AppDatabase {
   AppDatabase([QueryExecutor? executor]) : super(executor ?? _openConnection());
 
   @override
-  int get schemaVersion => 12;
+  int get schemaVersion => 13;
 
   @override
   MigrationStrategy get migration => MigrationStrategy(
@@ -227,6 +231,10 @@ class AppDatabase extends _$AppDatabase {
           if (from < 12) {
             await m.createTable(syncLogMailboxes);
           }
+          if (from < 13) {
+            await m.addColumn(accounts, accounts.verbose);
+            await m.addColumn(syncLogs, syncLogs.protocolLog);
+          }
         },
       );
 }
diff --git a/lib/data/imap/imap_client_factory.dart b/lib/data/imap/imap_client_factory.dart
index d845f2f..12abe22 100644
--- a/lib/data/imap/imap_client_factory.dart
+++ b/lib/data/imap/imap_client_factory.dart
@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:enough_mail/enough_mail.dart';
 import 'package:flutter/foundation.dart';
 
@@ -9,9 +11,18 @@ typedef ImapConnectFn = Future<ImapClient> Function(
   String password,
 );
 
+/// Zone value key signalling that a [StringBuffer] for protocol logging is
+/// active. When this key is non-null in the current zone, [connectImap]
+/// enables IMAP trace logging so the output is captured by the zone's
+/// print override.
+const verboseLogKey = #verboseProtocolLog;
+
 /// Opens an authenticated IMAP client for [account] using [username].
 ///
 /// Throws [Exception] if the account is not configured for SSL/TLS.
+///
+/// When the current [Zone] carries a [StringBuffer] under [verboseLogKey],
+/// IMAP trace logging is enabled so each command/response is captured there.
 Future<ImapClient> connectImap(
   Account account,
   String username,
@@ -22,9 +33,10 @@ Future<ImapClient> connectImap(
       'Unencrypted IMAP connections are not allowed. Enable SSL/TLS.',
     );
   }
+  final verboseBuffer = Zone.current[verboseLogKey] as StringBuffer?;
   final client = ImapClient(
     defaultResponseTimeout: const Duration(seconds: 20),
-    isLogEnabled: kDebugMode,
+    isLogEnabled: kDebugMode || verboseBuffer != null,
   );
   await client.connectToServer(account.imapHost, account.imapPort);
   await client.login(username, password);
diff --git a/lib/data/jmap/jmap_client.dart b/lib/data/jmap/jmap_client.dart
index 5a62884..8c34e6f 100644
--- a/lib/data/jmap/jmap_client.dart
+++ b/lib/data/jmap/jmap_client.dart
@@ -1,8 +1,11 @@
+import 'dart:async';
 import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:http/http.dart' as http;
 
+import '../imap/imap_client_factory.dart' show verboseLogKey;
+
 const _coreUsing = [
   'urn:ietf:params:jmap:core',
   'urn:ietf:params:jmap:mail',
@@ -125,6 +128,14 @@ class JmapClient {
         )
         .timeout(const Duration(seconds: 10));
 
+    final log = Zone.current[verboseLogKey] as StringBuffer?;
+    if (log != null) {
+      log.writeln('JMAP → POST $_apiUrl');
+      log.writeln(body);
+      log.writeln('JMAP ← ${resp.statusCode}');
+      log.writeln(resp.body);
+    }
+
     if (resp.statusCode != 200) {
       throw JmapException('API call failed (HTTP ${resp.statusCode})');
     }
diff --git a/lib/data/repositories/account_repository_impl.dart b/lib/data/repositories/account_repository_impl.dart
index d971112..79a5e0e 100644
--- a/lib/data/repositories/account_repository_impl.dart
+++ b/lib/data/repositories/account_repository_impl.dart
@@ -41,6 +41,7 @@ class AccountRepositoryImpl implements AccountRepository {
             accountType: Value(account.type.name),
             jmapUrl: Value(account.jmapUrl),
             username: Value(account.username),
+            verbose: Value(account.verbose),
           ),
         );
     await _storage.write(key: _passwordKey(account.id), value: password);
@@ -62,6 +63,7 @@ class AccountRepositoryImpl implements AccountRepository {
         accountType: Value(account.type.name),
         jmapUrl: Value(account.jmapUrl),
         username: Value(account.username),
+        verbose: Value(account.verbose),
       ),
     );
     if (password != null) {
@@ -99,5 +101,6 @@ class AccountRepositoryImpl implements AccountRepository {
         smtpPort: row.smtpPort,
         smtpSsl: row.smtpSsl,
         jmapUrl: row.jmapUrl,
+        verbose: row.verbose,
       );
 }
diff --git a/lib/data/repositories/sync_log_repository_impl.dart b/lib/data/repositories/sync_log_repository_impl.dart
index 4c7d706..ff2db7e 100644
--- a/lib/data/repositories/sync_log_repository_impl.dart
+++ b/lib/data/repositories/sync_log_repository_impl.dart
@@ -22,6 +22,7 @@ class SyncLogRepositoryImpl implements SyncLogRepository {
     required DateTime startedAt,
     required DateTime finishedAt,
     List<MailboxSyncStats> mailboxStats = const [],
+    String? protocolLog,
   }) async {
     await _db.transaction(() async {
       final logId = await _db.into(_db.syncLogs).insert(
@@ -37,6 +38,7 @@ class SyncLogRepositoryImpl implements SyncLogRepository {
               bytesTransferred: Value(bytesTransferred),
               startedAt: startedAt,
               finishedAt: finishedAt,
+              protocolLog: Value(protocolLog),
             ),
           );
       for (final s in mailboxStats) {
@@ -80,6 +82,7 @@ class SyncLogRepositoryImpl implements SyncLogRepository {
             bytesTransferred: r.bytesTransferred,
             startedAt: r.startedAt,
             finishedAt: r.finishedAt,
+            protocolLog: r.protocolLog,
             mailboxStats: mailboxRows
                 .map(
                   (m) => MailboxSyncStats(
diff --git a/lib/ui/screens/edit_account_screen.dart b/lib/ui/screens/edit_account_screen.dart
index 0263d16..98e5dd3 100644
--- a/lib/ui/screens/edit_account_screen.dart
+++ b/lib/ui/screens/edit_account_screen.dart
@@ -31,6 +31,7 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
   final _smtpHostCtrl = TextEditingController();
   final _smtpPortCtrl = TextEditingController();
   var _smtpSsl = false;
+  var _verbose = false;
   final _jmapUrlCtrl = TextEditingController();
 
   // -- "Try connection" state ------------------------------------------------
@@ -60,6 +61,7 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
     _smtpHostCtrl.text = account.smtpHost;
     _smtpPortCtrl.text = account.smtpPort.toString();
     _smtpSsl = account.smtpSsl;
+    _verbose = account.verbose;
     _jmapUrlCtrl.text = account.jmapUrl ?? '';
     setState(() => _loading = false);
   }
@@ -96,6 +98,7 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
       smtpSsl: _smtpSsl,
       jmapUrl:
           _jmapUrlCtrl.text.trim().isEmpty ? null : _jmapUrlCtrl.text.trim(),
+      verbose: _verbose,
     );
   }
 
@@ -160,6 +163,7 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
             smtpPort: updated.smtpPort,
             smtpSsl: updated.smtpSsl,
             jmapUrl: updated.jmapUrl,
+            verbose: updated.verbose,
           );
         }
       }
@@ -251,6 +255,16 @@ class _EditAccountScreenState extends ConsumerState<EditAccountScreen> {
                 onChanged: (v) => setState(() => _smtpSsl = v),
               ),
             ],
+            const Divider(height: 32),
+            SwitchListTile(
+              title: const Text('Verbose protocol logging'),
+              subtitle: const Text(
+                'Writes raw protocol traffic to the sync log. '
+                'Disable when not debugging.',
+              ),
+              value: _verbose,
+              onChanged: (v) => setState(() => _verbose = v),
+            ),
             if (_tryOk != null)
               Padding(
                 padding: const EdgeInsets.only(top: 8),
diff --git a/lib/ui/screens/sync_log_screen.dart b/lib/ui/screens/sync_log_screen.dart
index be5b354..e6ef83d 100644
--- a/lib/ui/screens/sync_log_screen.dart
+++ b/lib/ui/screens/sync_log_screen.dart
@@ -115,6 +115,31 @@ class _SyncLogTile extends StatelessWidget {
                     style: TextStyle(color: errorColor, fontSize: 12),
                   ),
                 ),
+              if (entry.protocolLog != null) ...[
+                const Padding(
+                  padding: EdgeInsets.only(top: 6, bottom: 2),
+                  child: Text(
+                    'Protocol log',
+                    style: TextStyle(fontSize: 12, color: Colors.grey),
+                  ),
+                ),
+                Container(
+                  width: double.infinity,
+                  padding: const EdgeInsets.all(8),
+                  decoration: BoxDecoration(
+                    color: Colors.black87,
+                    borderRadius: BorderRadius.circular(4),
+                  ),
+                  child: Text(
+                    entry.protocolLog!,
+                    style: const TextStyle(
+                      fontSize: 10,
+                      fontFamily: 'monospace',
+                      color: Colors.greenAccent,
+                    ),
+                  ),
+                ),
+              ],
             ],
           ),
         ),
diff --git a/test/unit/account_sync_manager_test.dart b/test/unit/account_sync_manager_test.dart
index b0b8c3e..a557b1d 100644
--- a/test/unit/account_sync_manager_test.dart
+++ b/test/unit/account_sync_manager_test.dart
@@ -202,6 +202,7 @@ class _CapturingSyncLogRepository implements SyncLogRepository {
     required DateTime startedAt,
     required DateTime finishedAt,
     List<MailboxSyncStats> mailboxStats = const [],
+    String? protocolLog,
   }) async {
     entries.add(
       SyncLogEntry(