Using the Apple Mail program version 3 under system OSX 10.5, click on the mail on toolbar

Select preferences.

Click on accounts at the top of the window (1), then click on the Server Settings under outgoing Mail server(2).

Then choose Edit Server List (1),

select Password behind authenication (1),

Put in your user name (2) and put in your password (3). Click OK and then close your preferences window saving changes.

You should then be able to send email.