Jan 29 16:24:28 mailserv dovecot: IMAP(username): unlink(/var/spool/mail/imap/user/username/Maildir/cur/Sent:2,ST) failed: Is a directory Something has created a directory called Sent inside Maldir/cur or Maildir/new. Dovecot treats it as a message and so it has added \Seen and \Deleted flags to it. Dovecot didn't create the Sent directory, look at other software/scripts you have.
Indeed.
There is one workaround I know which is: rm /var/spool/mail/imap/user/username/Maildir/dovecot.index* Delete the Sent* directory.
Seems like there used to be any software or exadmin which created those directories. I can not find out the source of it. I'm thinking about deleting all those but I am wondering if Maildir specification does allow any subdirectories in new/cur/tmp?
Thanks a lot!