I don't know how widespread this is, but at least a couple of 
academic sites with multiple subscribers to lists I manage have 
recently stopped delivering mail to "long-form" addresses -- 
i.e., mail addressed to (using my address as an example) 
[log in to unmask] simply comes back with an error 
message saying there are "no users at that domain; shortform 
addresses only." I suspect the users haven't been notified that 
their addresses have changed to (in my case) [log in to unmask], or 
haven't understood the notification.  I wind up manually 
changing all the addresses at that location. 

I've been told this may be part of the local postmaster trying 
to make spam and virus filtering more efficient, though I have 
to say I don't understand why that would be.

Two questions: (1) is anybody else encountering this? and (2) 
why, for days after I've changed the address, do I still get 
error messages from listserv saying that user (under the old 
long-form address) is being monitored?

-- Russ
St. Thomas University
http://www.StThomasU.ca/~hunt/