Normally you need to enable authentication to use mac.com as the outgoing mail server. I had that option checked, along with the option to use the login ID and password for authentication. Well turns out there must be a bug, because to finally get my email to send, I had to check the button "login as" instead, and enter my username and password manually. Walla, on all five computers, that fixed the problem.
Note: Why might one want to use this feature, well simple. If you have a portable computer, it allows you to send mail from where ever you connect, i.e. from home, work and friends houses. If you are using your ISPs outgoing mail server, you can only send mail when conected to your ISP.

