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Article: 1903
From: Grant Taylor
Date: 2008-10-06 15:42:18 -0400
Subject: Re: Milter-null in a split (mail-in vs mail-out) environment

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On 10/06/08 12:11, Anthony Howe wrote:
> No. It is very difficult to determine "direction" in SMTP. In SMTP, 
> everything looks incoming. The distinction is typically made in the 
> MTA as to which domains you accept.


Directionality is a concept that we humans assign to specific instances 
/ daemons.  I.e. we assign that this instance / daemon is used for X 
while another instance / daemon is used for Y.  Milters have no 
knowledge of what these directionalities are or how to do them.

My best bet is to define the milters as Mail_Filter(s) rather than 
Input_Mail_Filter(s) in side of Sendmail and then define which filters 
are used per instance / daemon via InputMailFilters on the 

However doing this may not work for the OP, see below for why.

> milter-null always inserts a X-Null-Tag header and if the message 
> crosses multiple servers using X-Null=Tag headers, then you get 
> multiple headers inserted. milter-null when it sees one or more 
> X-Null-Tag headers checks them ALL to see if any were generated by 
> that site.

It does not sound like you can get Milter-Null to just check a message 
with out inserting the X-Null header.  Thus it would not be possible to 
/not/ insert the header while handling inbound messages.

> Since it is a X- header, adding should not affect down stream servers 
> so I don't understand why their addition on the inbound stream should 
> be an issue.


Grant. . . .

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