Can't send mail from OS X Intel

[chrismorris]

I have a 2Gb MacBook running OS 10.4.10. No matter what combinations of SMTP authentication I put in the Apple Mail preferences (i.e. Password or MD5), I cannot send mail using my own domain in Plesk. To make matters worse, I find it confusing trying to understand the different mail settings between Preferences>Accounts>Account Information and Preferences>Accounts>Advanced

Help!
PS excuse me posting this earlier in the wrong forum.