Enterprise activation suddenly stops working

[notthegroundhog]

After successfully activating a number of new users and activating new phones for users who already had accounts with our enterprise server activation suddenly stopped working (on a Friday afternoon for a VP's phone that she had to have for the weekend).
Checked the phone can make calls.
Checked the phone can go on internet.
Checked corporate internet connection.
Checked the plan with carrier - supports enterprise email.
Checked services on Blackberry server and email server; all good.
Finally got blocked email report from spam filter.
All of the activation emails were being blocked. Had to whitelist Blackberry activation emails. Ours were coming from:

network@etp503102.etp.us.blackberry.net

Success!!! I hope this helps some poor soul.