Bouncing emails via procmail

[Paul M Foster <paulf@quillandmouse.com>]

Folks:

I'm running Debian Testing, exim and procmail. Probably half my email is 
spam, which procmail dutifully diverts into a spam folder. But I'm 
wondering if it would be possible to get procmail to actually "bounce" 
email back to senders when it's designated as spam. I know MTAs can do 
this, but I imagine it's a complicated process, since headers have to be 
examined, envelopes rewritten, etc. Also, to prevent loops, I'd have to 
add a header like X-Loop to the email and examine it on inbound emails.

Anyone know how to make procmail do this? Or is it a bad idea? Or what?

Paul