[Mimedefang] Powerful anti-spam rule :-)

[Dirk Mueller]

On Don, 07 Nov 2002, David F. Skoll wrote:

> For the following domains:
> 
> 	aol.com
> 	earthlink.net
> 	hotmail.com
> 	yahoo.com
> 
> Reject mail unless the relay machine resolves to one whose name
> ends in the same domain.

Thats a very old rule, and it really annoys many people using yahoo or 
hotmail addresses but not using their crowded and slow smtp servers. 

A much better filtering rule would be to have a validated sender address, 
which would be BTW a cool feature of Mimedefang (yeah, I should get around 
submitting a patch): 

"Verify" a sender address by connecting to the sender's MX server and trying 
to send a mail. check if the rcpt to: statement with the sender address is 
accepted. stop the session before the "data" command to avoid actually 
sending a mail. 

This will filter out i.e. all the forged-yahoo spam as yahoo will tell you 
at a rcpt to line if that email address exists or not. 

Of course there is some serious need for caching here, but this is trivial 
to do thanks to perl's tie'ed hashes. 


-- 
Dirk (received 76 mails today)