OT: Relay based on regex

[Paulo Roncon]

Hi, 

This is OT, but I'm struggling:
I need to:
Receive mail to: AS[3 letters]@mydomain.com  and to deliver to SA[3 letters]@mysub.mydomain.com
Ex: TO: ASaaa at mydomain.com DELIVER TO: SAaaa at mysub.mydomain.com

I have sendmail and mailscanner :)

I'm trying to use virtusertable but having trouble with regex... 
Changing to postfix is not an option...

Anyone can please help?

Thanks,
Paulo