I’ve had this problem on OS X server for the last 4 years, and only now have I figured it out. If an email has a X-UIDL header, then trying to upload it to an IMAP folder on OS X server, using Mail, will fail. This header is set by some POP servers but IMAP doesn’t implement it. So I don’t see why Cyrus cares if it is there. No error messages in mailaccess.log and every message I’ve tried with out the UIDL header has succeeded. Anyone have an answer here?