Auto-Reply Messages Missing DKIM Signature – Ending Up in Spam

[dowoFL]

Hi everyone,

recently a user called me, telling me that a lot of partners seem to not get the auto reply message he set up on his Exchange Server mailbox.

i did some investigation and found out, that a lot of these auto-reply messages where found in the recipients spam. The reason seems to be the missing DKIM:

Auto Reply Message:

Return-Path: <>
Authentication-Results: kundenserver.de; dkim=none

Compared to regular outgoing message from the same mailbox:

Return-Path: <***@***.**>
Authentication-Results: kundenserver.de; dkim=pass header.i=@***.**

First i thought that exchange maybe sends auto replys directly (and thus Proxmox cannot DKIM them) but the header clearly shows that also the auto-reply messages are sent via our proxmox:

Return-Path: <>
Authentication-Results: kundenserver.de; dkim=none
Received: from *********** ([**********]) by mx.kundenserver.de
(mxeue001 [212.227.**.**]) with ESMTPS (Nemesis) id 1MkFxp-1v4CwY1EAD-00abpn
for <*****@externalDomain.**>; Wed, 16 Jul 2025 16:15:35 +0200
[B]Received: from proxmox.*****.** (localhost.localdomain [127.0.0.1])[/B]
[B] by proxmox.******.** (Proxmox) with ESMTP id EB0064E0A69[/B]
for <*****@externalDomain.**>; Wed, 16 Jul 2025 16:15:34 +0200 (CEST)


Strangely, i am not sure if this should be the case, i also do not see the outgoing auto reply messages in the Proxmox Tracking Center.

Has anyone experienced something similar?
Or does someone know why Proxmox doesn't DKIM-sign auto-replies, even though it processes them?

Best,
dowoFL

 

[dowoFL]

Edit: After some more research i found this: https://bugzilla.proxmox.com/show_bug.cgi?id=2971

I will give that a try

As my colleague Shannon already hinted - in my experience most out-of-office autoreplies are sent with an empty envelope from address - as suggested in the relevant RFC [0], but do contain the address which is out-of-office in the From header (a.k.a RFC5322.From).
So signing a out-of-office mail with an address in the From header can be done by simply setting dkim-use-domain to 'header' at GUI->Configuration->Mail Proxy->DKIM - see section 4.7.10 at https://pmg.proxmox.com/pmg-docs/pmg-admin-guide.html#_mail_proxy_configuration