Originally Posted by bertiebassett
Few more ideas..
1) are you using external email scanning/filtering services (e.g. blackspider or messagelabs) - these types of services can mangle the activation emails.
A quick test for this is to remove the user from the BES and then try to do the activation on the handheld. Of course it won't work, but look in the users client inbox and see if the message from RIM/Blackberry shows up. If it does, then you're not filtering/blocking anything.
I'm having this issue right now with a new user and just got off the phone with RIM.