diff --git a/ics_mail_importer.py b/ics_mail_importer.py
index 0db10ce..351c151 100644
--- a/ics_mail_importer.py
+++ b/ics_mail_importer.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 """
-ics_mail_importer_env_v4.py
+ics_mail_importer_env_v5.py
 ---------------------------
 ICS-Importer für mailbox.org / CalDAV.
 
@@ -54,12 +54,17 @@ def env_bool(name: str, default: str = "false") -> bool:
 
 
 def is_newer_version_conflict(exc: Exception) -> bool:
-    message = str(exc)
-    return (
-        "412 Precondition Failed" in message
-        and "CAL-4121" in message
-        and "newer version of the appointment already exists" in message
-    )
+    message = str(exc or "").lower()
+    patterns = [
+        "412 precondition failed",
+        "cal-4121",
+        "newer version of the appointment already exists",
+        "concurrent modification",
+        "client sequence",
+        "actual sequence",
+    ]
+    matches = sum(1 for p in patterns if p in message)
+    return matches >= 2
 
 
 def import_ics_to_caldav(ics_bytes: bytes, uid_hash: str):