Mail Delivery failure

[Karen]

I have one specific user that constantly receives email replies for
undeliverable emails to an unknown address in which he never sent. Can
someone explain why and how to fix it?

 

[Brian Tillman]

I have one specific user that constantly receives email replies for
undeliverable emails to an unknown address in which he never sent. Can
someone explain why and how to fix it?

There's nothing that can be done. Somewhere on the Internet, someone who
has your user's address in his or her address book has been infected with
malware. This infection uses the addresses on that machine to fake the
sender address as it attempts to send more copies of itself out. The
receiving mail router (wherever that is) can't deliver the bugger's attempt
at self-replication and so sends a rejection message back to the only
address it has: your user's. Since it's someone else's machine that's
infected, there's nothing your user can do to fix it, other that try to
create a rule that will delete the bounces.