diff --git a/app/email_utils.py b/app/email_utils.py
index dc387985..0b8396b6 100644
--- a/app/email_utils.py
+++ b/app/email_utils.py
@@ -636,7 +636,7 @@ def copy(msg: Message) -> Message:
     try:
         # prefer the unicode way
         return email.message_from_string(msg.as_string())
-    except (UnicodeEncodeError, KeyError):
+    except (UnicodeEncodeError, KeyError, LookupError):
         LOG.warning("as_string() fails, try to_bytes")
         return email.message_from_bytes(to_bytes(msg))