i explain you the method i use in bes 3.6 (im going to install bes4 but i have not an srp id yet...
i dont know if it will help you, but in my opinion the migration of a bb device from one BES to another is a little difficult sometimes... i have migrated 20 bbs and i met very diferent problems... :s
1) remove the user from the old BES server and when it prompts to delete blackberry info from mailbox select "yes". probably you have not the older bes running... then you should remove the user from the new server and deleting the blackberry information from inbox (if it prompts).
2) connect the blackberry to the BES server via USB (make sure the BES server detects the connection (properties, connect, detect).
3) add the user to the BES server
4) right click in the user and click properties... a prompt should appear saying that the BB connected to the bes is not the one of the user and if you want to assign that BB to that user. Make sure is the correct user and click "YES"
5) send the policy and all stuff you want
6) if you use MDS enable it for the user and try to navigate via BES the first time with the BB connected via USB to the BES. if it doesnt run, try to resend the policy and try it again.
if it doesnt work...
7) turn off the bb device (fetch the battery too), and turn on it again...
Sometimes you have to reinstall some applications if you have your own applications installed.
in the email redirection i have never met problems.... make sure the mapi configuration is correct...
i think BB devices caches a lot of things of the configuration and sometimes is difficult to make the migration... good luck.
i have learned all of this alone, maybe there are much better methods... i dont know... and when i begin with bes4.0 ixxx314;l told you