we are using mailcow-dockerized already now for three years. DKIM, SPF, DMARC all working fine.
But to some destinations (only very few ones) mails cannot be transmitted because their mail servers are checking if the HELO is a valid host. But the HELO that mailcow is using is for whatever reason not the name of our mail server (i.e mail.example.com) but a unique string followed by localdomain, for example helo=5036e8a19602.localdomain and that is of course not a valid server name and the other mailserver is then rejecting it with …said: 450 4.7.1
<5036e8a19602.localdomain>: Helo command rejected: Host not found (in reply to RCPT TO command)
No problems with the big mail providers (google, yahoo, gmx, outlook, …) because they are checking if the sender IP is valid as an authenitcated sender.
Authentication-Results: spf=pass (sender IP is 81.xxx.xxx.xxx)
smtp.mailfrom=example1.com; example2.com; dkim=pass (signature was verified)
header.d=example1.com;example2.com; dmarc=pass action=none
Received-SPF: Pass (protection.outlook.com: domain of example1.com
designates 81.xxx.xxx.xxx as permitted sender)
Received: from 5036e8a19602.localdomain (81.xxx.xxx.xxx) by
DB5EUR01FT022.mail.protection.outlook.com (10.152.4.244) with Microsoft SMTP
Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
15.20.3784.11 via Frontend Transport; Fri, 22 Jan 2021 17:18:39 +0000
How can I fix it that the name of our mail server is used in the HELO and not a unique string with localdomain?
In the mailcow.conf the variable MAILCOW_HOSTNAME is set (MAILCOW_HOSTNAME=mail.example1.com)
In data/conf/postfix/main.cf I do see a line:
mydestination = localhost.localdomain, localhost
adding a extra.cf in data/conf/postfix with
mydestination = mail.example1.com, localhost.example1.com, localhost
did not help to solve the problem.
After a restart (docker-compose down, docker-compose up -d) just the unique string has changed:
Received: from b3c1c839e19b.localdomain
In the logs I do see that a replace is done:
root@xyz:/var/abc/mailcow-dockerized# docker-compose logs |grep b3c1c839e19b.localdomain
postfix-mailcow_1 | Jan 22 20:14:18 b3c1c839e19b postfix/cleanup: 6922B464124: replace: header Received: from bad5accc21aa (mailcowdockerized_sogo-mailcow_1.mailcowdockerized_mailcow-network [172.22.1.248])??(Authenticated sender: email@example.com)??by b3c1c839e19b.localdomain (Postcow) wit from mailcowdockerized_sogo-mailcow_1.mailcowdockerized_mailcow-network[172.22.1.248]; firstname.lastname@example.org email@example.com proto=ESMTP helo=<bad5accc21aa>: Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPA id 6922B464124??for firstname.lastname@example.org; Fri, 22 Jan 2021 20:14:18 +0100 (CET)