fix: use UID-based IMAP commands and batch STORE operations to fix T-Online BYE errors

Agent-Logs-Url: https://github.com/christianlouis/InboxConverge/sessions/d01a05d3-31e1-4aca-b75d-c4e63b7e5af0

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

CHANGELOG.md

@@ -21,9 +21,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Dashboard "Recent Processing Runs" table replaced with a per-account **Mailbox Status** view: each account now shows its last-check status (OK / Error / Pending), relative last-check time, any error message, and lifetime processed/failed counters. The noisy per-run table is gone; full activity history remains available on the Logs page.
 - Stats cards updated: "Emails Forwarded Today" → "Emails Processed" (all-time total from account records); "Errors" → "Accounts with Errors" (count of accounts currently showing an error).
+- **IMAP: switched to UID-based commands** (`UID SEARCH`, `UID FETCH`, `UID STORE`) instead of volatile sequence-number-based commands.  Sequence numbers shift whenever other messages are expunged, causing the wrong messages to be targeted and triggering "Too many invalid IMAP commands" errors on strict servers like T-Online.  UIDs remain stable for the lifetime of a mailbox.
 ### Fixed
 - Provider logos now appear on the Mail Accounts page: `provider_name` is correctly saved when creating accounts via the provider wizard and propagated through backend/frontend schemas.
 - Fetch-emails button now shows a text label ("Fetch"), a descriptive tooltip, a "Fetching…" loading state, and a brief green "Queued!" confirmation after the action completes.
+- **IMAP: eliminated redundant per-message `STORE +FLAGS \Seen`** — RFC822 FETCH implicitly marks a message as `\Seen` on IMAP servers, making the extra round-trip unnecessary.  This reduces the total command count by *N* per polling cycle.
+- **IMAP: batch `STORE +FLAGS \Deleted`** — when `delete_after_forward` is enabled, all successfully fetched UIDs are now marked for deletion in a single `UID STORE uid1,uid2,…` command instead of one command per message.
+- **IMAP: batch re-marking of stale UIDs** — UIDs already tracked in the database that still appear as UNSEEN on the server (e.g. because a previous STORE failed) are now re-marked `\Seen` with a single batch command instead of one STORE per message.
+- **IMAP: graceful BYE handling** — the IMAP client is now stored in a variable so the `finally` block always attempts a clean `logout()`.  If the server has already sent `BYE` and closed the connection the logout failure is swallowed silently, preventing it from masking the original error.
 
 ## v0.3.2 (2026-03-28)
 

backend/app/services/mail_processor.py

@@ -263,10 +263,26 @@ class MailProcessor:
     async def _fetch_imap_emails(
         self, max_count: int, already_seen_uids: Set[str]
     ) -> Tuple[List[bytes], List[str]]:
-        """Fetch emails via IMAP, marking each message \\Seen to prevent re-fetch."""
+        """Fetch emails via IMAP using UID-based commands.
+
+        UIDs are stable identifiers that do not change when other messages are
+        expunged, unlike IMAP sequence numbers.  Sequence-number-based FETCH /
+        STORE commands can target the wrong message mid-session and cause
+        servers to report "Too many invalid IMAP commands" (as seen with
+        t-online).  This implementation:
+
+        * Uses ``UID SEARCH``, ``UID FETCH``, and ``UID STORE`` throughout.
+        * Re-marks already-processed UIDs as \\Seen in a single batch command
+          instead of one STORE per message.
+        * Relies on the implicit \\Seen flag set by RFC822 FETCH so no
+          additional per-message STORE is needed for newly fetched mail.
+        * Batches the \\Deleted STORE into a single command when
+          ``delete_after_forward`` is enabled.
+        """
         emails: List[bytes] = []
         new_uids: List[str] = []
 
+        imap_client = None
         try:
             # Create IMAP client
             if self.account.protocol == MailProtocol.IMAP_SSL:
@@ -282,70 +298,122 @@ class MailProcessor:
             await imap_client.login(self.account.username, self.password)
             await imap_client.select("INBOX")
 
-            # Search for unseen messages only
+            # UID SEARCH returns stable UIDs instead of volatile sequence numbers.
-            response = await imap_client.search("UNSEEN")
+            response = await imap_client.uid("search", "UNSEEN")
-            message_ids = response.lines[0].split()
+            if (
+                response.result != "OK"
+                or not response.lines
+                or not response.lines[0].strip()
+            ):
+                logger.info(f"Found 0 unread messages for account {self.account.id}")
+                # logout is handled by the finally block below
+                return emails, new_uids
 
-            # Limit to max_count
+            all_unseen_uids: List[bytes] = response.lines[0].split()
-            message_ids = message_ids[:max_count]
+
+            # Limit to max_count before doing any further work.
+            all_unseen_uids = all_unseen_uids[:max_count]
 
             logger.info(
-                f"Found {len(message_ids)} unread messages for account {self.account.id}"
+                f"Found {len(all_unseen_uids)} unread messages for account "
+                f"{self.account.id}"
             )
 
-            # Fetch each message
+            # Split into stale UIDs (already in our DB but still UNSEEN on the
-            for msg_id in message_ids:
+            # server — e.g. a previous STORE failed) and genuinely new UIDs.
-                uid_str = msg_id.decode() if isinstance(msg_id, bytes) else str(msg_id)
+            stale_uid_bytes: List[bytes] = []
-
+            uids_to_fetch: List[bytes] = []
-                # Skip messages already tracked in our DB
+            for uid in all_unseen_uids:
+                uid_str = uid.decode() if isinstance(uid, bytes) else str(uid)
                 if uid_str in already_seen_uids:
-                    logger.debug(
+                    stale_uid_bytes.append(uid)
-                        f"Skipping already-processed IMAP message {uid_str} "
+                else:
-                        f"for account {self.account.id}"
+                    uids_to_fetch.append(uid)
-                    )
-                    # Still mark as Seen so it doesn't show up in UNSEEN searches
-                    await imap_client.store(msg_id, "+FLAGS", "\\Seen")
-                    continue
 
+            # Re-mark stale UIDs as \Seen in a single batch STORE command so
+            # they stop appearing in UNSEEN searches without consuming one
+            # round-trip per message.
+            if stale_uid_bytes:
+                uid_set = b",".join(stale_uid_bytes).decode()
                 try:
-                    response = await imap_client.fetch(msg_id, "(RFC822)")
+                    await imap_client.uid("store", uid_set, "+FLAGS", "\\Seen")
+                except Exception as e:
+                    logger.warning(
+                        f"Failed to re-mark stale messages as \\Seen for account "
+                        f"{self.account.id}: {e}"
+                    )
 
-                    # Extract email data from response
+            # Fetch each new message.  RFC822 FETCH implicitly sets \Seen on
-                    email_data = None
+            # the server so no extra STORE per message is required.
-                    for line in response.lines:
+            fetched_uids: List[bytes] = []
-                        if isinstance(line, bytes) and b"RFC822" in line:
+            for uid in uids_to_fetch:
-                            # Find the email content
+                uid_str = uid.decode() if isinstance(uid, bytes) else str(uid)
-                            start_idx = line.find(b"{")
+                try:
-                            if start_idx != -1:
+                    fetch_response = await imap_client.uid("fetch", uid_str, "(RFC822)")
-                                # Email data is in the next parts
+
-                                continue
+                    # Extract raw email bytes from the FETCH response lines.
-                        elif isinstance(line, bytes) and not line.startswith(b"*"):
+                    # A UID FETCH response looks like:
-                            email_data = line
+                    #   [b'<seq> (UID <uid> RFC822 {<size>}', <email_bytes>, b')']
-                            break
+                    # Skip the header line (contains "RFC822") and grab the
+                    # first substantive bytes value.
+                    email_data: Optional[bytes] = None
+                    for line in fetch_response.lines:
+                        if not isinstance(line, bytes):
+                            continue
+                        if b"RFC822" in line:
+                            continue
+                        if line.startswith(b"*"):
+                            continue
+                        if line in (b")", b""):
+                            continue
+                        email_data = line
+                        break
 
                     if email_data:
                         emails.append(email_data)
                         new_uids.append(uid_str)
-
+                        fetched_uids.append(uid)
-                        # Always mark as Seen after fetching so the message is
+                    else:
-                        # not picked up again on the next UNSEEN search.
+                        logger.warning(
-                        await imap_client.store(msg_id, "+FLAGS", "\\Seen")
+                            f"No email data extracted for UID {uid_str} on "
-
+                            f"account {self.account.id}"
-                        if self.account.delete_after_forward:
+                        )
-                            await imap_client.store(msg_id, "+FLAGS", "\\Deleted")
 
                 except Exception as e:
-                    logger.error(f"Error fetching message {msg_id}: {e}")
+                    logger.error(
+                        f"Error fetching message UID {uid_str} for account "
+                        f"{self.account.id}: {e}"
+                    )
 
-            # Expunge deleted messages
+            # Batch-mark fetched messages for deletion if configured (one STORE
-            if self.account.delete_after_forward:
+            # command covers all UIDs instead of N individual commands).
-                await imap_client.expunge()
+            if self.account.delete_after_forward and fetched_uids:
-
+                uid_set = b",".join(fetched_uids).decode()
-            await imap_client.logout()
+                try:
+                    await imap_client.uid("store", uid_set, "+FLAGS", "\\Deleted")
+                    await imap_client.expunge()
+                except Exception as e:
+                    logger.warning(
+                        f"Failed to delete messages for account "
+                        f"{self.account.id}: {e}"
+                    )
 
+        except MailFetchError:
+            raise
         except Exception as e:
-            logger.error(f"Error fetching IMAP emails: {e}")
+            logger.error(
+                f"Error fetching IMAP emails for account {self.account.id}: {e}"
+            )
             raise MailFetchError(f"IMAP fetch error: {str(e)}")
+        finally:
+            # Always attempt a clean logout.  If the server already sent BYE
+            # the logout call will fail silently rather than masking the real
+            # error.
+            if imap_client is not None:
+                try:
+                    await imap_client.logout()
+                except Exception:
+                    pass
 
         return emails, new_uids
 

backend/tests/unit/test_mail_processor_imap.py

@@ -0,0 +1,383 @@
+"""
+Unit tests for the UID-based IMAP fetch logic in MailProcessor.
+
+These tests verify that _fetch_imap_emails:
+  - Uses UID SEARCH / UID FETCH / UID STORE commands (not sequence numbers)
+  - Batches stale-UID re-marking into a single STORE command
+  - Does NOT issue a per-message STORE for Seen (RFC822 sets it implicitly)
+  - Batches Deleted STORE into a single command when delete_after_forward=True
+  - Handles an empty UNSEEN result without error
+  - Handles individual message fetch failures gracefully
+  - Always attempts logout in the finally block
+"""
+
+import pytest
+from unittest.mock import AsyncMock, MagicMock, call, patch
+
+
+# ---------------------------------------------------------------------------
+# Helpers to build lightweight fakes
+# ---------------------------------------------------------------------------
+
+
+def _make_account(
+    protocol="imap_ssl",
+    host="imap.example.com",
+    port=993,
+    username="user@example.com",
+    delete_after_forward=False,
+    account_id=1,
+):
+    """Return a minimal MailAccount-like mock."""
+    from app.models.database_models import MailProtocol
+
+    account = MagicMock()
+    account.id = account_id
+    account.host = host
+    account.port = port
+    account.username = username
+    account.delete_after_forward = delete_after_forward
+    account.protocol = (
+        MailProtocol.IMAP_SSL if protocol == "imap_ssl" else MailProtocol.IMAP
+    )
+    return account
+
+
+def _make_imap_response(result="OK", lines=None):
+    """Return an object that looks like an aioimaplib ImapResponse."""
+    resp = MagicMock()
+    resp.result = result
+    resp.lines = lines if lines is not None else [b""]
+    return resp
+
+
+def _make_fetch_response(uid_str: str, email_bytes: bytes):
+    """
+    Simulate the lines that aioimaplib returns for a UID FETCH (RFC822) call.
+
+    The typical structure is:
+      [b'<seq> (UID <uid> RFC822 {<size>}', <email_data>, b')']
+    """
+    header = f"1 (UID {uid_str} RFC822 {{12345}}".encode()
+    return _make_imap_response(result="OK", lines=[header, email_bytes, b")"])
+
+
+# ---------------------------------------------------------------------------
+# Tests
+# ---------------------------------------------------------------------------
+
+
+class TestFetchImapEmailsUidCommands:
+    """Verify UID-based command usage in _fetch_imap_emails."""
+
+    @pytest.fixture
+    def processor(self):
+        from app.services.mail_processor import MailProcessor
+
+        account = _make_account()
+        return MailProcessor(account=account, decrypted_password="secret")
+
+    @pytest.fixture
+    def mock_imap(self):
+        """A mock aioimaplib client whose async methods are AsyncMock."""
+        client = MagicMock()
+        client.wait_hello_from_server = AsyncMock()
+        client.login = AsyncMock()
+        client.select = AsyncMock()
+        client.uid = AsyncMock()
+        client.logout = AsyncMock()
+        return client
+
+    async def test_uses_uid_search_not_plain_search(self, processor, mock_imap):
+        """SEARCH should be issued as UID SEARCH UNSEEN."""
+        mock_imap.uid.return_value = _make_imap_response(result="OK", lines=[b""])
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            await processor._fetch_imap_emails(10, set())
+
+        # uid("search", "UNSEEN") must be the first uid() call
+        first_uid_call = mock_imap.uid.call_args_list[0]
+        assert first_uid_call == call("search", "UNSEEN")
+
+    async def test_no_messages_returns_empty(self, processor, mock_imap):
+        """Empty UNSEEN result should return empty lists without error."""
+        mock_imap.uid.return_value = _make_imap_response(result="OK", lines=[b""])
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            emails, uids = await processor._fetch_imap_emails(10, set())
+
+        assert emails == []
+        assert uids == []
+
+    async def test_fetches_new_message_via_uid_fetch(self, processor, mock_imap):
+        """New messages should be fetched with UID FETCH, not plain FETCH."""
+        raw_email = b"From: sender@example.com\r\nSubject: Test\r\n\r\nBody"
+        uid = b"42"
+
+        def uid_side_effect(command, *args):
+            if command == "search":
+                return _make_imap_response(result="OK", lines=[uid])
+            if command == "fetch":
+                return _make_fetch_response(uid.decode(), raw_email)
+            return _make_imap_response()
+
+        mock_imap.uid = AsyncMock(side_effect=uid_side_effect)
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            emails, new_uids = await processor._fetch_imap_emails(10, set())
+
+        assert emails == [raw_email]
+        assert new_uids == ["42"]
+
+        # The fetch call should use UID FETCH
+        fetch_call = [
+            c for c in mock_imap.uid.call_args_list if c.args[0] == "fetch"
+        ]
+        assert len(fetch_call) == 1
+        assert fetch_call[0] == call("fetch", "42", "(RFC822)")
+
+    async def test_no_per_message_store_for_seen(self, processor, mock_imap):
+        """RFC822 implicitly marks \\Seen; no extra STORE per message is needed."""
+        raw_email = b"From: a@b.com\r\n\r\nHello"
+        uids = b"10 11 12"
+
+        def uid_side_effect(command, *args):
+            if command == "search":
+                return _make_imap_response(result="OK", lines=[uids])
+            if command == "fetch":
+                uid_str = args[0]
+                return _make_fetch_response(uid_str, raw_email)
+            return _make_imap_response()
+
+        mock_imap.uid = AsyncMock(side_effect=uid_side_effect)
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            emails, new_uids = await processor._fetch_imap_emails(10, set())
+
+        # No STORE command should have been called (delete_after_forward=False)
+        store_calls = [
+            c for c in mock_imap.uid.call_args_list if c.args[0] == "store"
+        ]
+        assert store_calls == [], "Expected no STORE commands for \\Seen"
+
+        assert len(emails) == 3
+        assert new_uids == ["10", "11", "12"]
+
+    async def test_stale_uids_batched_in_single_store(self, processor, mock_imap):
+        """UIDs already in already_seen_uids must be re-marked in one batch STORE."""
+        # Two messages: one stale (already in DB), one new
+        raw_email = b"From: x@y.com\r\n\r\nNew mail"
+
+        def uid_side_effect(command, *args):
+            if command == "search":
+                return _make_imap_response(result="OK", lines=[b"5 6"])
+            if command == "fetch":
+                return _make_fetch_response(args[0], raw_email)
+            return _make_imap_response()
+
+        mock_imap.uid = AsyncMock(side_effect=uid_side_effect)
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            emails, new_uids = await processor._fetch_imap_emails(
+                10, already_seen_uids={"5"}  # UID 5 is stale
+            )
+
+        # Only UID 6 is new
+        assert new_uids == ["6"]
+        assert len(emails) == 1
+
+        store_calls = [
+            c for c in mock_imap.uid.call_args_list if c.args[0] == "store"
+        ]
+        # Exactly one STORE for the stale UID
+        assert len(store_calls) == 1
+        assert store_calls[0] == call("store", "5", "+FLAGS", "\\Seen")
+
+    async def test_multiple_stale_uids_batched_together(self, processor, mock_imap):
+        """Multiple stale UIDs should be sent as a comma-separated set."""
+
+        def uid_side_effect(command, *args):
+            if command == "search":
+                return _make_imap_response(result="OK", lines=[b"1 2 3 4"])
+            if command == "fetch":
+                return _make_fetch_response(args[0], b"email data")
+            return _make_imap_response()
+
+        mock_imap.uid = AsyncMock(side_effect=uid_side_effect)
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            await processor._fetch_imap_emails(10, already_seen_uids={"1", "2"})
+
+        store_calls = [
+            c for c in mock_imap.uid.call_args_list if c.args[0] == "store"
+        ]
+        assert len(store_calls) == 1
+        # The UID set string should contain both stale UIDs (order may vary)
+        uid_set_arg = store_calls[0].args[1]
+        parts = set(uid_set_arg.split(","))
+        assert parts == {"1", "2"}
+
+    async def test_delete_after_forward_uses_single_batch_store(self):
+        """delete_after_forward=True must issue one UID STORE \\Deleted command."""
+        from app.services.mail_processor import MailProcessor
+
+        account = _make_account(delete_after_forward=True)
+        processor = MailProcessor(account=account, decrypted_password="s")
+
+        mock_imap = MagicMock()
+        mock_imap.wait_hello_from_server = AsyncMock()
+        mock_imap.login = AsyncMock()
+        mock_imap.select = AsyncMock()
+        mock_imap.expunge = AsyncMock()
+        mock_imap.logout = AsyncMock()
+
+        def uid_side_effect(command, *args):
+            if command == "search":
+                return _make_imap_response(result="OK", lines=[b"7 8"])
+            if command == "fetch":
+                return _make_fetch_response(args[0], b"raw email")
+            return _make_imap_response()
+
+        mock_imap.uid = AsyncMock(side_effect=uid_side_effect)
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            emails, new_uids = await processor._fetch_imap_emails(10, set())
+
+        assert new_uids == ["7", "8"]
+
+        store_calls = [
+            c for c in mock_imap.uid.call_args_list if c.args[0] == "store"
+        ]
+        # Exactly one STORE for deletion covering both UIDs
+        assert len(store_calls) == 1
+        uid_set_arg = store_calls[0].args[1]
+        parts = set(uid_set_arg.split(","))
+        assert parts == {"7", "8"}
+        assert store_calls[0].args[2] == "+FLAGS"
+        assert store_calls[0].args[3] == "\\Deleted"
+        # expunge must also be called
+        mock_imap.expunge.assert_awaited_once()
+
+    async def test_individual_fetch_failure_does_not_abort(self, processor, mock_imap):
+        """A single message fetch error should be logged but not stop processing."""
+        raw_email = b"From: ok@example.com\r\n\r\nOK"
+
+        call_count = {"count": 0}
+
+        def uid_side_effect(command, *args):
+            if command == "search":
+                return _make_imap_response(result="OK", lines=[b"20 21"])
+            if command == "fetch":
+                call_count["count"] += 1
+                if call_count["count"] == 1:
+                    raise Exception("Connection dropped by server")
+                return _make_fetch_response(args[0], raw_email)
+            return _make_imap_response()
+
+        mock_imap.uid = AsyncMock(side_effect=uid_side_effect)
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            emails, new_uids = await processor._fetch_imap_emails(10, set())
+
+        # Second message should still be processed
+        assert len(emails) == 1
+        assert new_uids == ["21"]
+
+    async def test_logout_called_even_on_connection_error(self, processor, mock_imap):
+        """logout() must be attempted even when the connection drops mid-session."""
+        mock_imap.uid = AsyncMock(side_effect=Exception("BYE server gone"))
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            from app.services.mail_processor import MailFetchError
+
+            with pytest.raises(MailFetchError):
+                await processor._fetch_imap_emails(10, set())
+
+        mock_imap.logout.assert_awaited_once()
+
+    async def test_logout_failure_does_not_mask_error(self, processor, mock_imap):
+        """If logout itself raises, the original MailFetchError should propagate."""
+        mock_imap.uid = AsyncMock(side_effect=Exception("server gone"))
+        mock_imap.logout = AsyncMock(side_effect=Exception("logout also failed"))
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            from app.services.mail_processor import MailFetchError
+
+            with pytest.raises(MailFetchError):
+                await processor._fetch_imap_emails(10, set())
+
+    async def test_respects_max_count_limit(self, processor, mock_imap):
+        """Only max_count messages should be processed."""
+        raw_email = b"From: a@b.com\r\n\r\nHi"
+
+        def uid_side_effect(command, *args):
+            if command == "search":
+                # 5 messages available
+                return _make_imap_response(result="OK", lines=[b"1 2 3 4 5"])
+            if command == "fetch":
+                return _make_fetch_response(args[0], raw_email)
+            return _make_imap_response()
+
+        mock_imap.uid = AsyncMock(side_effect=uid_side_effect)
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4_SSL",
+            return_value=mock_imap,
+        ):
+            emails, new_uids = await processor._fetch_imap_emails(3, set())
+
+        assert len(emails) == 3
+        assert new_uids == ["1", "2", "3"]
+
+    async def test_plain_imap_uses_imap4_not_ssl(self):
+        """Non-SSL IMAP accounts must use IMAP4, not IMAP4_SSL."""
+        from app.services.mail_processor import MailProcessor
+
+        account = _make_account(protocol="imap")
+        processor = MailProcessor(account=account, decrypted_password="pw")
+
+        mock_imap = MagicMock()
+        mock_imap.wait_hello_from_server = AsyncMock()
+        mock_imap.login = AsyncMock()
+        mock_imap.select = AsyncMock()
+        mock_imap.logout = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=_make_imap_response(result="OK", lines=[b""])
+        )
+
+        with patch(
+            "app.services.mail_processor.aioimaplib.IMAP4",
+            return_value=mock_imap,
+        ) as mock_cls:
+            await processor._fetch_imap_emails(10, set())
+            mock_cls.assert_called_once()

docs/TODO.md

@@ -4,6 +4,7 @@ Comprehensive task breakdown for repository improvements and production readines
 
 ## ✅ Recently Completed
 
+- [x] **IMAP reliability: switched to UID-based commands** — `_fetch_imap_emails` now uses `UID SEARCH`, `UID FETCH`, and `UID STORE` throughout.  Sequence numbers are volatile (they shift on expunge), causing "Too many invalid IMAP commands" on strict servers (e.g. T-Online).  UIDs are stable.  The per-message `STORE +FLAGS \Seen` (redundant — RFC822 sets it implicitly) and per-message `STORE +FLAGS \Deleted` are replaced with single batch commands.  Stale already-seen UIDs are re-marked `\Seen` in one command.  Logout is now in a `finally` block so a mid-session `BYE` is handled gracefully.
 - [x] **Dashboard redesign**: Replaced noisy "Recent Processing Runs" table with a per-account "Mailbox Status" view showing last-check status (OK/Error/Pending), relative timestamp, error messages, and lifetime counters. Stats cards updated to show all-time processed count and accounts-with-errors count.
 - [x] **Provider logos now saved on account creation**: `provider_name` field added to `MailAccountCreate` and `MailAccountUpdate` schemas (backend and frontend). `ProviderWizard` now passes `provider_name` in its `onSelect` callback; `AddMailAccountModal` stores it so logos are displayed correctly on the accounts page.
 - [x] **Fetch button UX improvements**: The "fetch emails" button on the accounts page now shows a "Fetch" text label for clarity, a tooltip explaining its purpose, a spinning "Fetching…" state during the API call, and a brief green "Queued!" confirmation after success.