This guide is made using Apple Mail 4, but might apply to other versions.
Open Mail, select File and Add Accounts
Check all details in Account Summary. If they are not as follows, click Go Back and change
Account Description: Optional
Incoming mail server: pop3.spintel.net.au
Outgoing mail server: smtp.spintel.net.au
Tick: Take account online.
Once all the details have been confirmed, click Create. Mail is now ready for use.