I was trying to send a message to someone using the link in their profile, but it was not present. My profile when viewed by someone else does not have the send a message button either. But a few people still have it.
I should be able to receive Private Messages. I have the box checked, but why does it not show on my buddies account? He has his checked as well and I can't message him.
Have you sent him a PM before? He may have accidentally blocked you: Block Sender is right next to Delete Message. He'll have to unblock you, but I don't remember offhand how to do it.