[Mailman-Users] Strange Wiki entry for Postfix Tuning

Brad Knowles brad at shub-internet.org
Thu Aug 6 21:49:28 CEST 2009

on 8/4/09 5:11 AM, Stefan Förster said:

> So, what is the reason for that setting? From man 5 postconf:
> ,----[ man 5 postconf | less +/^smtp_mx_session_limit ]
> | smtp_mx_session_limit (default: 2)
> |
> |     The maximal number of SMTP sessions per delivery request before
> |     giving up or delivering to a fall-back relay host, or zero (no
> |     limit). This restriction ignores sessions that fail to complete
> |     the SMTP initial handshake (Postfix version 2.2 and earlier) or
> |     that fail to complete the EHLO and TLS handshake (Postfix version
> |     2.3 and later).
> |
> |     This feature is available in Postfix 2.1 and later.
> `----
> While I can certainly imagine larger sites having somewhere between
> five to ten MXs, 100 seems a bit... oversized.

The way I read this, it has nothing to do with the number of MXes you 
have.  It has to do with how many SMTP delivery sessions you'll attempt 
over the same connection before you drop the connection and re-connect 
(if you have more than this number of deliveries left), and that 
re-connection may well end up going to a different MX.

This helps avoid conditions where you get locked into a particular MX 
that is slow, and that slows down all your delivery to that site, for as 
long as you have mail for that site.

But I would expect Ralf to know the answer to this question better than 
I do -- after all, it has been a number of years since I wrote that, and 
at my age, the memory starts to go.

Brad Knowles <brad at shub-internet.org>
LinkedIn Profile: <http://tinyurl.com/y8kpxu>

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