diff --git a/internal/imap/scheduler.go b/internal/imap/scheduler.go
index 86ecf65..062e6bd 100644
--- a/internal/imap/scheduler.go
+++ b/internal/imap/scheduler.go
@@ -398,7 +398,17 @@ func (s *Scheduler) syncFolder(
 		if err != nil {
 			return 0, 0, fmt.Errorf("imap scheduler: uid search incremental %q: %w", folder, err)
 		}
-		uids = searchData.AllUIDs()
+		// Defensive re-filter: some IMAP servers mishandle open-ended "N:*"
+		// UID ranges and return UIDs below N anyway (observed against
+		// q.sysops.de — "UID SEARCH UID 22:*" on a 21-message mailbox
+		// returned [21] instead of an empty set). Trusting that blindly
+		// makes the sync loop rediscover the same top message as "new"
+		// forever, every cycle. Never trust the server's range filtering.
+		for _, uid := range searchData.AllUIDs() {
+			if uid >= minUID {
+				uids = append(uids, uid)
+			}
+		}
 	} else {
 		// First sync or post-UIDVALIDITY-reset: fetch everything.
 		searchData, err := c.UIDSearch(&imapv2.SearchCriteria{}, nil).Wait()