The maillog shows that it can't authenticate-
01:15:06 ispc1 imapd: Disconnected, ip=[::ffff:10.0.0.6], time=5
Mar 5 01:20:01 ispc1 getmail: Initializing SimpleIMAPRetriever:email@example.com:143:
Mar 5 01:20:01 ispc1 imapd: Connection, ip=[::ffff:10.0.0.6]
Mar 5 01:20:01 ispc1 imapd: LOGIN FAILED, user=testuser, ip=[::ffff:10.0.0.6]
I understand Fedora is experimental, so I don't mind if things like this happen. I see that courier is now used in ispconfig3 and dovecot was used in ispconfig2. Maybe courier is not authenticating to the correct database?