If you would like to use secure (SSL) settings within your mail client, please ensure you use the below settings:

NOTE - in order to use an SSL without the "Certificate Warning" error, you will need to purchase an SSL, which you can do so via this page : http://hosting-australia.com/security/ssl-certs

Incoming Server: mail.[DOMAINNAME]
IMAP Port: 993
POP3 Port: 995

Outgoing Server: mail.[DOMAINAME]
SMTP Port: 465

Type of Encrypted Connection: SSL

Please see http://clients.hosting-australia.com/knowledgebase.php?action=displaycat&catid=1 and use the above settings in conjuction with these setup guides.