I am currently doing some research on MTAs used by the Checkmk community. This question is primarily directed to installations that are mostly for mail forwarding, but I am happily listening to anyone running “real” mail systems where SMTP and IMAP go hand in hand and all kind of filtering (milter, spam scoring) is used.
Background is that we are currently discussing improving mail server/mail queue monitoring. And we are discussing suggestions we give our users on how to send mails from their Checkmk server. This is currently mostly Postfix on larger installs and nullmailer on smaller installs.
For the drop only MTAs, we see that ssmtp (last major 16 years ago, orphaned on many distributions), nullmailer (last major 7 years ago, starting to crash) and esmtp (last major 15 years ago) are essentially unmaintained. Thus dma and msmtp have been gaining traction and we want to reflect this in monitoring.
Which of those are you using? And did I forget to mention another one?
On my CMK RAW RockyLinux 9.5 box with i am using Postfix as MTA.
Its configured to only receive on localhost and forward to my mailgateway ( Proxmox Mail Gateway)
Which will either send it out to an external mailbox (customer), or send to my internal mailsystem ( Groupwise) … or both ofcourse.
I expected that from you. Building a safe, secure drop mail Postfix is no witchcraft, still it has pitfalls for people who are not doing mail admin at least from time to time.
On most of our leaf systems (including all of our CheckMK sites) we use nullmailer with authenticated relaying through our central mail server, which in turn runs Postfix. Most of our customers with Linux systems with MTAs on them use Postfix, some systems use nullmailer as well. We used to see Exim here and there, but we actually don’t anymore.
We also have a handful of customers running Proxmox Mail Gateway. Like their other products this is a lot of standard OSS software based on Debian together with their own UIs/glue code. In the case of PMG Postfix is the MTA under the hood, too. Therefore such machines can be monitored with the regular agent.
Regarding Proxmox Mail Gateway,
Previously i had a pure Postfix gateway with an antispam solution (DSPAM) which worked perfectly for me, but when upgrading i was unable to recreate the setup due to dependancies.
So in the end i stepped towards PMG , and that has payed off, but had to implement some custom changes under the hood ( not able to do so via gui).
Changes needed were to split incoming/outgoing mail per ip, as some legacy applications would not accept port 26 (unable to change in application)
But as said, that is pure postfix config under the hood.
Did put in an enhancement request for it, but it was deemed to exotic without more request and has not yet been honored.
