How to disable additional outgoing email headers?

Technical assistance
1

Infos:

  • Used Zammad version: 6.5.2
  • Used Zammad installation type: docker-compose
  • Operating system: Linux
  • Browser + version: Chrome 140.0.7339.208

Expected behavior:

  • Reply to an email gets sent via Proton Mail Bridge

Actual behavior:

  • Replies get sent via Proton Mail Bridge just like the test Email

Steps to reproduce the behavior:

  • Setup a Zammad instance and Proton Mail Bridge
  • Connect the Bridge as an Email account with the Account Details provided by the bridge
  • Test Email gets sent sucessfully
  • receive an Email
  • reply to that Email from within the ticket
  • ERRO[Oct 14 07:04:29.312] Send mail failed. error="failed to send message: failed to create draft: 422 POST https://mail-api.proton.me/mail/v4/messages: Dieser Wert sollte eine der folgenden Bedingungen erfüllen: [1] ExternalID ist ungültig. [2] ExternalID erlaubt nur ''. (Code=2001, Status=422)" pkg=smtp wich translates to "This value should meet one of the following conditions: [1] ExternalID is invalid. [2] ExternalID only allows ‘’.
  • → Settings → Email → Accounts → Outbound shows error #<Net::SMTPFatalError: Net::SMTPFatalError>

Question:

  • Is it possible to configure Zammad to not send any additional headers, like it does in the test emails? I don’t really like the idea of having to use another email relay just to remove the headers.
2

Sorry, but there’s no such header. You cannot adjust the headers Zammad adds. They should be default headers anyway so your mail bridge might be the issue.

Default headers from a ticket reply looks like so:

Return-Path: <sales@xxxx.de>
Delivered-To: marcel@xxxx.com
Received: from mail.xxxx.de
	by cc.tha-systems.de. with LMTP
	id tpOEJ0iKAmkwOh8AEEYImA
	(envelope-from <sales@xxxx.de>)
	for <marcel@xxxx.com>; Wed, 29 Oct 2025 22:42:32 +0100
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=thg-yt.de;
	s=tha-230501; t=1761774152;
	bh=pumOIUP3yrKJHnHWSzi0porE7hEFQQq2YlcZSrP+vLg=;
	h=Date:From:To:In-Reply-To:References:Subject:From;
	b=M2D8cth1TLdYLtBE6JP0A/QdisdmTxDDnbRb+fAwL8yQRygesG8lEYpbJu+dnuoog
	 LBlh8raWZFk1z3u5N6jziMsvFi92/yggijR44dqjAKU1FfMzbkJIY5UagZNKdQAu8m
	 lNLqsj5Rx8Hqet2He0a2AlSBqjgPfBECo1j7CmYqW7afOy9mSbFCz1s7xVmvYROSbf
	 uC/5RyFEjvMNajCliZ+r8CappuUhPylA8S5htW5nrlQRD5BQZjTKb9RANHzJjJ40eu
	 nP7cm1wvIQXXnJd7zU0hvK8STISF+Yc6xBkGSWxkYMi11WRFm1LSp9C0sKFh5ddNqn
	 /pelFtbaxwK6A==
Date: Wed, 29 Oct 2025 22:42:38 +0100
From: Marcel Herrguth via Enjoy THG <sales@xxxx.de>
To: marcel@xxxx.com
Message-ID: <20251029214235.15.46cb6dbb-61c4-4b57-9160-e19034ff7ef1@thg-howto-series.tha.srv>
In-Reply-To: <3C325A70-37ED-4DCA-893F-8521ACA659E8@xxxx.com>
References: <5A6DC467-7495-4BF3-8749-0AA37FECFEC7@xxxx.com>
 <3C325A70-37ED-4DCA-893F-8521ACA659E8@xxxx.com>
 <3C325A70-37ED-4DCA-893F-8521ACA659E8@xxxx.com>
Subject: RE: Invoices [Ticket#31014]
Mime-Version: 1.0
Content-Type: multipart/mixed;
 boundary="--==_mimepart_69028a4e51d43_1e9139a8622e0";
 charset=UTF-8
Content-Transfer-Encoding: 7bit
Organization: XXXX
X-Powered-By: Zammad - Helpdesk/Support (https://zammad.org/)

Sending test mails like so:

Message-ID: <69028b2d9528f_1e51394856971@thg-howto-series.mail>
Subject: Zammad Getting started Test Email #497eac5016edc4642a4d
Mime-Version: 1.0
Content-Type: text/plain;
 charset=UTF-8
Content-Transfer-Encoding: 7bit
X-Zammad-Test-Message: #497eac5016edc4642a4d
X-Zammad-Ignore: true
X-Zammad-Fqdn: thg-howto-series.tha.srv
X-Zammad-Verify: true
X-Zammad-Verify-Time: 2025-10-29T21:46:21Z
X-Loop: yes
Precedence: bulk
Auto-Submitted: auto-generated
X-Auto-Response-Suppress: All