Ports 110, 143 are disabled by default for security reason (they don't encrypt connections), please use port 995 (POP3 over TLS) and 993 (IMAP over TLS) instead.
If you still want to use ports 110/143 (again, it's not recommended), try this tutorial:
http://www.iredmail.org/wiki/index.php? … t.STARTTLS