Select File, Add Account.
Username: Your full address. Eg: firstname.lastname@example.org
Incoming Server: mail.yourdomain.com
Outgoing Server: mail.yourdomain.com
(Outgoing) SMTP Server Requires password authentication
SSL should NOT be checked for both incoming and outgoing mail.
The incoming mail server Port should be set to 110
The outgoing mail server Port should be set to 587