I am using the catchall method. If one of our users sends an email to a invalid account at say yahoo.com it sends back an email from MAILER-DAEMON@mydomain.com to nobody@mydomain.com which I have aliased to a POP3 account so I find out it did not make it to its destination but the sender does not. Is there a way so that the sender can find out his or her email did not make it to its intended recipient when using the catchall method?