Download only certain POP messages

Normally when you check for new messages in a POP account it downloads all of the new messages. However, you could configure Thunderbird to only download headers using tools -> account settings -> server settings-> fetch headers only. You could then create a message filter that tests whether the sender was in your address book and checkmark the "fetch body from POP server" action. Or create some other rule to determine whether you want to download the message body.