OpenDKIM and Postfix milter protocol version

From: Steve Jenkins <>
Date: Mon, 22 Aug 2011 09:37:17 -0700

I received a question through my blog today that I hadn't thought
about. The question was:

" I noticed that you suggest to set the milter_protocol to 2 in Postfix 2.6+ uses a different higher default (6) for the
protocol version. Since we're running other milters, I'm worried that
lowering the protocol could cause issues to the mail server. Postfix
does not seem to support configuration of a per-milter protocol

"Any idea why OpenDKIM require protocol version 2, or if it can also
work with version 6? Documentation on how the protocol changes from
version to version is sparse at best..."

I hadn't really thought about that before. When I first installed
OpenDKIM, I was running Postfix 2.3.3 (the default on CentOS 5), but
now I'm running 2.8. According to the Postfix Milter docs:

It says:

Milter protocol version

As Postfix is not built with the Sendmail libmilter library, you may
need to configure the Milter protocol version that Postfix should use.
The default version is 6 (before Postfix 2.6 the default version is

    # Postfix ≥ 2.6
    milter_protocol = 6
    # 2.3 ≤ Postfix ≤ 2.5
    milter_protocol = 2
If the Postfix milter_protocol setting specifies a too low version,
the libmilter library will log an error message like this:

application name: st_optionneg[xxxxx]: 0xyy does not fulfill action
requirements 0xzz
The remedy is to increase the Postfix milter_protocol version number.
See, however, the limitations section below for features that aren't
supported by Postfix.

Any Postfix users currently running their milter_protocol at 6 instead
of 2? How is that affecting OpenDKIM (if at all?) I can't access my VM
until later this afternoon, so I can't test it myself yet.


Received on Mon Aug 22 2011 - 16:37:31 PST

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