bounced messages: "mrgate@firnux"

["Alice H. Yucht" <YUCHT@ZODIAC.RUTGERS.EDU>]

Every time I send a message to LM_NET, I get a bounced back copy from
MRGATE@FIRNIUX.  marked as undeliverable, not such address.
Is there any way to eliminate this address, so it doesn't keep bouncing back?
Am I the only one with this problems?