Thanks for your reply. I don't think its the SquirrelMail client as I can see rejected login attempts in the Dovecot log. I think Webuzo didn't create the username correctly - any idea how can I find out?
Aug 17 10:25:35 imap-login: Info: Aborted login (auth failed, 1 attempts in 4 secs): user=<hakim>, method=PLAIN, rip=54.169.225.28, lip=172.31.4.78