Spam email on Exchange!!! Help!!

Hello everyone,

Few of our clients are receiving a large volume of spam. The email says it’s coming from “KIDS JUKE BOX CALGARY”. However from the header of the email you can tell it’s coming our Email server(MS exchange 2003).

I checked the “Queues” folder in “Exchange system Manager” and I found hundreds of these messages stuck in the “smtp connector” folders.

What exactly happened?? and how do I stop this.
Please advise.
Thanks
Canaan