Oh, "Gurus of the Exchange World," I am running Exchange 5.5 on a NT 4 Server. One of our users has been sending email to an invalid email address (non existent mailbox), but non of his mail has been bounced back by our Exchange server. Our domain is (user)@csical.com He has been sending email to a non-existent user @csical.com, but nothing gets bounced back. Since we only have 15 mailboxes in our organization, it has been very easy to check and verify that the user really does not exist. The only thing I can say is that I installed a Microsoft patch which cured my problem with NDRs a few months back (KB-837794). Could this be affecting our server in that it won't bounce invalid mail addresses back to the user? Is there a setting somewhere that I can check? Any advice is greatly appreciated!! Thanks, --Jason Davis