Thanks to Bill and Benny for the pointer to
https://www.postfix.org/DEBUG_README.html#mail.
Using tcpdump I figured out that a monitoring task using OpenSsl (with
hardcoded mail.example.org) was reusing the same ip (via NAT). You´d call it
gremlins
Joachim
-Ursprüngliche Nachricht-
Von: Bill Cole via Postfix-users
Gesendet: Montag, 12. Februar 2024 16:18
An: Joachim Lindenberg via Postfix-users
Betreff: [pfx] Re: postfix alternating between mail.example.com and real
hostname?
On 2024-02-12 at 07:07:03 UTC-0500 (Mon, 12 Feb 2024 13:07:03 +0100) Joachim
Lindenberg via Postfix-users is rumored to have
said:
> I haven´t seen this before, but at present my mail server is kind of
> alternating between mail.example.com and the real hostname (or someone
> is spoofing my IP-address which I doubt).
It is not at all clear what you actually mean by that. Any MTA has a
potentially complicated collection of different "identities" used in different
context. E.g. in Postfix you've got origin domain names, destination domain
names, hostnames used in MX records, and a hostname used in HELO/EHLO
greetings.
Or is the 'alternating' happening in DNS? We cannot know...
> All configuration files I checked indicate the correct setting and
> postconf myhostname returns the correct name. Thus I am wondering
> whether this might be caused by a recent change of postfix, which
> happens tob e 3.5.23 – the mail server is a mailcow-dockerized
> instance which still uses images based on debian-bullseye.
>
> Any idea for the cause and a fix?
My guess: Gremlins.
You might get more useful answers by including the illuminating information
described at https://www.postfix.org/DEBUG_README.html#mail
in the section titled "Reporting problems to postfix-users@postfix.org"
--
Bill Cole
b...@scconsult.com or billc...@apache.org (AKA @grumpybozo and many
*@billmail.scconsult.com addresses) Not Currently Available For Hire
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