Originally Posted by DennyEller
Would nice if you could filter to only allow mail from people in your address book.
You can do this from the device.
Go to Options > Security Options > Firewall. Place a check next to Personal Email, and then under exceptions, place a check next to contacts.
That is running OS 6. OS 4.5 might be slightly different. It may be labeled Blackberry Internet Service instead of Personal Email. I don't have any OS 4.5 devices available to test.