My email address that I wanted to sign up with has a hyphen in the first part of it (and is an edu address).  I was not getting the activation emails.  Waited 24 hours, checked all spam folders.  As soon as I changed it to a different email address (gmail), it worked fine.

I'm afraid to change it back to the edu address because I wont get any emails at all.

I have not heard of this before.
If the forum descriminates against certain email addresses then it would be a function of the SMF forum hosting service and unfortunately beyond our control.
Not much help but my best suggestion is that you continue to use an email address that is known to work without issue.

Tweakie.