email digest?

would it be possible for a user to subscribe to a board. and whenever a message has been posted on that board, they get an email saying blah blah blah. and be able to unsubscribe and so on. or subscribe to a thread?

yep, rangersfan wrote one yesterday and it works on my forum

http://www.vbulletin.com/forum/showthread.php?threadid=2822