fix(send_queue): 修复重复消息 ID 的失败重排并清理 MIME

- 投递成功后清空 `mime_base64`，避免已投递队列项保留原始 MIME。
- 当同一 `message_id` 的旧队列项已达到最大失败次数时，允许复用并重新入队。
- 补充测试覆盖已投递项清理与终态失败重排场景。

apps/api/internal/app/app_test.go

@@ -894,6 +894,13 @@ func TestSendQueueRecoversStaleSendingItems(t *testing.T) {
 	if status != sendQueueStatusDelivered {
 		t.Fatalf("queue status=%q, want delivered", status)
 	}
+	var mimeBase64 string
+	if err := a.db.QueryRow(`SELECT mime_base64 FROM send_queue WHERE id=?`, queueID).Scan(&mimeBase64); err != nil {
+		t.Fatal(err)
+	}
+	if mimeBase64 != "" {
+		t.Fatal("delivered queue item should not retain raw MIME")
+	}
 }
 
 func TestSubmissionAuthRequiresMailboxPasswordAndSendPermission(t *testing.T) {
@@ -1082,6 +1089,46 @@ func TestSubmissionSentCopyDedupesByMessageID(t *testing.T) {
 	}
 }
 
+func TestSubmissionRequeuesTerminalFailedDuplicateMessageID(t *testing.T) {
+	a := newTestApp(t)
+	a.cfg.SMTPHost = "127.0.0.1"
+	a.cfg.SMTPPort = "1"
+	user, mb, err := a.authenticateSubmission(context.Background(), "admin@lanqin.local", "ChangeMe123!")
+	if err != nil {
+		t.Fatal(err)
+	}
+	raw := "From: admin@lanqin.local\r\nTo: person@example.com\r\nSubject: requeue\r\nMessage-ID: <requeue@example.test>\r\n\r\nbody"
+	if err := a.submitSMTPMessage(context.Background(), user, mb, mb.Address, []string{"person@example.com"}, strings.NewReader(raw)); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := a.db.Exec(`UPDATE send_queue SET status=?,attempt_count=max_attempts,next_attempt_at=?,last_error='terminal' WHERE mailbox_id=? AND message_id=?`, sendQueueStatusFailed, a.now().UTC().Add(time.Hour).Format(time.RFC3339Nano), mb.ID, "<requeue@example.test>"); err != nil {
+		t.Fatal(err)
+	}
+
+	host, port, received := startCapturingSMTP(t, 1)
+	a.cfg.SMTPHost = host
+	a.cfg.SMTPPort = port
+	if err := a.submitSMTPMessage(context.Background(), user, mb, mb.Address, []string{"person@example.com"}, strings.NewReader(raw)); err != nil {
+		t.Fatal(err)
+	}
+	if err := a.processDueSendQueue(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	select {
+	case <-received:
+	case <-time.After(2 * time.Second):
+		t.Fatal("requeued terminal failure was not relayed")
+	}
+	var status string
+	var attemptCount int
+	if err := a.db.QueryRow(`SELECT status,attempt_count FROM send_queue WHERE mailbox_id=? AND message_id=?`, mb.ID, "<requeue@example.test>").Scan(&status, &attemptCount); err != nil {
+		t.Fatal(err)
+	}
+	if status != sendQueueStatusDelivered || attemptCount != 1 {
+		t.Fatalf("queue status=%q attempts=%d, want delivered attempts=1", status, attemptCount)
+	}
+}
+
 func TestSubmissionAllowsAuthorizedAliasSendAs(t *testing.T) {
 	a := newTestApp(t)
 	ctx := context.Background()

apps/api/internal/app/send_queue.go

@@ -66,18 +66,38 @@ func (a *App) enqueueSend(ctx context.Context, in sendQueueInput) (string, error
 	}
 	id := newID("snd")
 	messageID := strings.TrimSpace(in.MessageID)
+	mimeBase64 := base64.StdEncoding.EncodeToString(in.MIMEBytes)
+	recipientsJSON := jsonEncode(dedupeEmails(in.Recipients))
 	_, err := a.db.ExecContext(ctx, `INSERT OR IGNORE INTO send_queue(id,user_id,mailbox_id,sent_message_id,message_id,source,mail_from,header_from,recipients_json,mime_base64,status,next_attempt_at,created_at,updated_at)
 		VALUES(?,?,?,?,?,?,?,?,?,?,?,?,?,?)`,
-		id, in.UserID, in.MailboxID, in.SentMessageID, messageID, in.Source, normalizeEmail(in.MailFrom), normalizeEmail(in.HeaderFrom), jsonEncode(dedupeEmails(in.Recipients)), base64.StdEncoding.EncodeToString(in.MIMEBytes), sendQueueStatusQueued, now.Format(time.RFC3339Nano), now.Format(time.RFC3339Nano), now.Format(time.RFC3339Nano))
+		id, in.UserID, in.MailboxID, in.SentMessageID, messageID, in.Source, normalizeEmail(in.MailFrom), normalizeEmail(in.HeaderFrom), recipientsJSON, mimeBase64, sendQueueStatusQueued, now.Format(time.RFC3339Nano), now.Format(time.RFC3339Nano), now.Format(time.RFC3339Nano))
 	if err != nil {
 		return "", err
 	}
 	if strings.TrimSpace(messageID) != "" {
-		var existingID string
+		var existingID, status string
-		if err := a.db.QueryRowContext(ctx, `SELECT id FROM send_queue WHERE mailbox_id=? AND source=? AND message_id=?`, in.MailboxID, in.Source, messageID).Scan(&existingID); err != nil {
+		var attemptCount, maxAttempts int
+		if err := a.db.QueryRowContext(ctx, `SELECT id,status,attempt_count,max_attempts FROM send_queue WHERE mailbox_id=? AND source=? AND message_id=?`, in.MailboxID, in.Source, messageID).Scan(&existingID, &status, &attemptCount, &maxAttempts); err != nil {
 			return "", err
 		}
 		if existingID != id {
+			if status == sendQueueStatusFailed && attemptCount >= maxAttempts {
+				_, err := a.db.ExecContext(ctx, `UPDATE send_queue SET user_id=?,sent_message_id=?,mail_from=?,header_from=?,recipients_json=?,mime_base64=?,status=?,attempt_count=0,next_attempt_at=?,last_error='',updated_at=?,delivered_at=NULL WHERE id=? AND status=? AND attempt_count>=max_attempts`,
+					in.UserID, in.SentMessageID, normalizeEmail(in.MailFrom), normalizeEmail(in.HeaderFrom), recipientsJSON, mimeBase64, sendQueueStatusQueued, now.Format(time.RFC3339Nano), now.Format(time.RFC3339Nano), existingID, sendQueueStatusFailed)
+				if err != nil {
+					return "", err
+				}
+				a.recordSendAudit(ctx, sendAuditQueued, sendQueueStatusQueued, sendAuditInput{
+					QueueID:       existingID,
+					UserID:        in.UserID,
+					MailboxID:     in.MailboxID,
+					SentMessageID: in.SentMessageID,
+					Source:        in.Source,
+					MailFrom:      in.MailFrom,
+					HeaderFrom:    in.HeaderFrom,
+					Recipients:    in.Recipients,
+				})
+			}
 			return existingID, nil
 		}
 	}
@@ -191,7 +211,7 @@ func (a *App) processSendQueueItem(ctx context.Context, id string) {
 		return
 	}
 	now := a.now().UTC().Format(time.RFC3339Nano)
-	if _, err := a.db.ExecContext(ctx, `UPDATE send_queue SET status=?,delivered_at=?,updated_at=?,last_error='' WHERE id=?`, sendQueueStatusDelivered, now, now, item.ID); err != nil {
+	if _, err := a.db.ExecContext(ctx, `UPDATE send_queue SET status=?,delivered_at=?,updated_at=?,last_error='',mime_base64='' WHERE id=?`, sendQueueStatusDelivered, now, now, item.ID); err != nil {
 		a.log.Warn("failed to mark send queue delivered", "id", item.ID, "error", err)
 		return
 	}