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Article: 1918
From: Steve Freegard
Date: 2008-12-03 11:31:40 -0500
Subject: Re: milter-null and DSN/MDN messages

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Hi Greg,

Greg Matthews wrote:
> Hi Steve...
> Steve Freegard wrote:
>> Either pass -one-rcpt-per-null in the start-up options or edit your 
>> milter-null.cf file (defaults to /etc/mail/milter-null.cf) and change 
>> the same option as it currently defaults to +one-rcpt-per-null (+ = on, 
>> - = off) see http://www.snertsoft.com/sendmail/milter-null
> I was wary of doing this as I didn't necessarily want to turn this 
> functionality off for all domains but a quick look at the logs over the 
> last week shows that this doesn't seem particularly effective as an 
> anti-spam technique. I think it is almost entirely hitting these 
> automated forwards.

It's an RFC conformance option - the RFC states that messages from the 
null-sender should only be to a single recipient and it's only really 
cases like yours that might be a problem, so it's really for 
defence-in-depth - the spammers don't do this now, but they might start 
sometime in the future:

[root@mail ~]# echo STAT | nc localhost 25 | grep -P '( 
214-2.0.0 age=1212139 (14 00:42:19)
214-2.0.0 015 CLIENTS=5197232 (100.00%)
214-2.0.0 099 one-rcpt-per-null=0 (0.00%)

> Thanks for the response - didnt realise you lurked here too!

No problem - Anthony and I are good friends since our work on 
BarricadeMX together, so I have knowledge of the milters as well as some 
of it is common code (such as one-rcpt-per-null) and they also share the 
same configuration syntax.  So I lurk here and post whenever anything 
appears that I can help with.


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