i had major email issues on my BB over the past weekend. TMO opened a ticket with RIM and RIM helped me to work out the issue.
I received a status from RIM saying email could not be delivered to my blackberry.net email address; and the yahoo and gmail worked. the tech support asked me to remove the blackberry.net address; re-added it; and tried.
it worked after i readded it.
-- TMO Blackberry 8700g since 09/24/2006