Using the standard IMAP port. 993 and SSL.
See below code from the mail server logs as its logging in ok.
Aug 14 14:06:57 box dovecot: imap-login: Login: user=<support@domain.com>, method=PLAIN, rip=::1, lip=::1, mpid=18947, TLS, session=<98lrIEUd8gAAAAAAAAAAAAAAAAAAAAAB>
Aug 14 14:06:57 box dovecot: imap(support@domain.com): Disconnected: Logged out in=158 out=704
Aug 14 14:10:02 box dovecot: imap-login: Login: user=<support@domain.com>, method=PLAIN, rip=0.0.0.0, lip=0.0.0.0, mpid=19054, TLS, session=<mMRyK0UdCADA/kyk>
Aug 14 14:10:02 box dovecot: imap(support@domain.com): Disconnected: Logged out in=97 out=568