Ok, that's what I'm thinking.
SMF has a built-in function to use a formal SMTP mailer rather than the forwarding route that AOL doesn't like (because of the spammers).
I'm going to test this, but I believe we can simply put in the SMTP settings of our domain, and the registration/validation emails would then be sent as formal emails from our domain and not the forwarding that AOL, etc., doesn't like. I think .Mac has a problem with some forwards as well.
I also found a post on another forum which allows Google mail to be used, which is even better. The validation email would have whatever valid Google address you setup as the return, and it would allow you to easily track the emails that have been sent for validation. Since many forum admins are using GMail these days for their forums, this could be an ideal solution. A ton of storage, and an easy 'search' feature to be able to track down any problems.