Mac Mail - Can't SEND e-mail - FIX it!
Not all versions of Mac Mail have 'outgoing server settings' in the same spot. However you should be able to easily find it. If you can't, google it :) Note: I've seen cases where the Mail app itself has corrupt data, so the only way to solve it is to re-install the app/Mac OS completely. In those cases, even with the correct settings, it still won't work.