Unfortunately, forum email was not working for quite some time. Users did not receive notifications on new posts, did not receive confirmation messages for registrations or could not use the forum to send email to other users.
It has been fixed now and should work again. There was a backlog of email messages in the queue that has now been sent, some of them a bit dated now, I'm afraid.
This mishap probably had to do with the forum server having moved to new hardware and the mail system apparently wasn't properly configured on the new one. I'm sorry for not noticing this and not fixing it earlier.