[Mimedefang] Detecting bogus envelope senders?

[Fernando Gleiser]

'm getting lots of spam pretending to come from internal addresses.
They're specially nasty on accounts that due to their nature (support,
sales and the like) can't be too agressive in their spam filtering.

So far I had some success stopping them using filter_sender to restrict
which IPs those accounts can send mail from. I know they'll never send 
mail from outside our network, but now it seems that spammers are using 
bogus MAIL FROM: addresses and forging the From: header as one of those 
accounts.

I think I need something like

if (From is one of those special accounts)
 	if (envelope != from)
 		reject messaje

go on with the normal filtering.

Is there an easy way I can do this?

Thanks in advance

 		Fer