Activated Blackberry Enterprise Services mail account on my 8520. A small oversight caused me a day or two of delay in this configuration. I had an Exchange mail filter/rule that moves mail to a different folder, when certain conditions are met. Unfortunately, the handshake email sent by the Blackberry Enterprise Service activation met that criteria and the mail is moved to a different folder right away. However, the activation process expected the mail in the Inbox. This caused a couple of iterations of the activation process. Finally, I figured out what is going wrong and temporarily disabled the specific filters. Once that is done, the rest of the process is a cakewalk.
Now the Blackberry 8520 is syncing with multiple email accounts.