Depending on your software version, your screens may appear a bit different, but the setting will be the same.
Go to: Mail -> Preferences
Enter your information as above, only substitute your own domain name for "methownet.com". For example, if your domain name is geenapples.com and your name is Biff, you would enter: mail.greenapples.com in the mail server fields, and firstname.lastname@example.org in the user name field.
(note: Mac may require you to enter your user name this way instead: biff+greenapples.com)
Click the *Server Settings...* button
(it may look or be named differently on some systems)
Authentication should be "Password" and enter your full email address as your User Name.
(note: Mac may require you to enter your user name this way instead: biff+yourdomain.com)
Server port: 25, and DONT check the SSL box.
The important part of this screen is the bottom: Authentication: None, Port: 110 and No to SSL.
(note: these screens were borrowed from wheresmywireless.com)