[Exim] 550:Address not know at this ite

Hi

I am currently running exim3.22 on Solaris2.8.
I have a mail message that keeps bouncing and filling up the mail
server.
I have tried removing the the message from the queue but that
doesn't help, it just keeps coming back.

The error message I get when trying to deliver the message is :
"   SMTP error from remote mailer after RCPT 
TO:<tanjas20@???>:
    host gauss.cam.wits.ac.za [146.141.21.250]: 550 Address not known at this site."

The server gauss.cam.wits.ac.za is a valid mail server, but the id tanjas20 does not
exist on that server which is what is probably causing the message to bounce.

Is there any way to stop it .
Is there a filter I could possibly write.

Any help would be greatly appreciated.
Thanks
Cheers
sherona