Exim+ClamAV: how to temporary block virus sender automatically?

[Alexander Vasenin aka BlackSir]

Hi all!
I'm working in a little ISP company. We are using Exim+ClamAV(+some other stuff) for our mail servers. Because of Mydoom,Netsky & etc shit we are proxy all outgoing SMTP connections through our mail server(via reverse natd + some ipfw rules). Everything works fine - all viruses rejected by our MTA, but it produces a heavy load. Is there any way in Exim to temporary block virus senders IP automatically to reduce load on MTA(and assist clients to heal themself, becouse now they aren't know anything about tons of blocked virus e-mails from their computers)?

Alexander Vasenin aka BlackSir