Unable to append a message to a folder: The message has been rejected by the IMAP server.
Possible causes:
- One or more messages have an empty subject line or a line that has a subject that has only a “Re:”
- The message has a malformed or corrupted header
Resolution:
To solve it you need to delete or move the offending messages to a different folder.
Additional Information:
- https://github.com/rgrove/larch/issues/24