Filter envelope sender not from address to prevent new spam attack

Hi,

We've been using TMDA for challenge/response on our server successfully for 
several years.

Version: tmda-1.1.9-1

Recently, we've been getting spam like this:
	Return-Path: <[email protected]>
	From: [email protected]
	To: [email protected]

Because user2 has user1 whitelisted, the spam gets through without challenge.

What I'd like to happen is to specify a filter that uses the return path 
(envelope sender) if that's specified and only use the From address if there 
is no return path.

We use Exim and its config will prevent email being delivered with no valid 
return path if the From user says it's our domain but the sending server is 
not our domain.

I guess we could improve the Exim config to handle the mismatched envelope 
sender and From address, but it's actually valid in some cases for this to 
happen.  For example, user1 might send to user2 from his gmail account.  The 
>From is still our local domain.

Is there any way for TMDA's filter to check the return path in preference to 
the From Address but fallback to From if no return path is present?

-- 
Russell Robinson ([email protected])
Author of Tectite FormMail and FormMailEncoder/Decoder
Root Software (www.tectite.com)

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