Running your own mail and groupware server can be challenging. I recently had to re-create my own setup from the ground, and this blog post is the first in a series describing all the steps.
Running mail servers on your own
Running your own mail server sounds tempting: having control over a central piece of your own communication does sound good, right?
But that can be quite challenging: The mail standards are not written for today’s way to operate technology. Many of them are vague, too generic to be really helpful, or just not deployed widely in reality. Other things are not standardized at all so you have to guess and test (max message sizes, anyone?). Also, even the biggest providers have their own interpretations of the standards and sometimes aggressively ignore them which you are forced to accept.
Also there is the spam problem: there is still a lot of spam out there. And since this is an ongoing fight mail server admins have to constantly adjust their systems to newest tricks and requirements. Think of SPF, DKIM, DMARC and DANE here.
Last but not least the market is more and more dominated by large corporations. If your email is tagged as spam by one of those, you often have no way to figure out what the problem is – or how to fix it. They simply will not talk to you if you are not of equal size (or otherwise important). In fact, if I have a pessimistic look into the future of email, it might happen that all small mail service providers die and we all have to use the big services.
Thus the question is if anyone should run their own mail server at all. Frankly, I would not recommend it if you are not really motivated to do so. So be warned.
However, if you do decide to do that on your own, you will learn a lot about the underlying technology, about how a core technology of “the internet” works, how companies work and behave, and you will have huge control about a central piece of today’s communication: mail is still a corner stone of today’s communication, even if we all hate it.
To better understand my motivation it helps to know where I come from: In my past job at credativ I was project manager for a team dealing with large mail clusters. Like, really large. The people in the team were and are awesome folks who *really* understand mail servers. If you ever need help running your own open source mail infrastructure, get them on board, I would vouch for them anytime.
And while I never reached and never will reach the level of understanding the people in my team had, I got my fair share of knowledge. About the the technological components, the developments in the field, the challenges and so on. Out of this I decided at some point that it would be fun to run my own mail server (yeah, not the brightest day of my life, in hindsight…).
Thus at some point I set up my own domain and mail server. And right from the start I wanted more than a mail server: I wanted a groupware server. Calendars, address books, such a like. I do not recall how it all started, and how the first setup looked like, but I know that there was a Zarafa instance once, in 2013. Also I used OpenLDAP for a while, munin was in there as well, even a trac service to host a git repository. Certificates were shipped via StartSSL. Yeah, good times.
In summer 2017 this changed: I moved Zarafa out of the picture, in came SOGo. Also, trac was replaced by Gitlab and that again by Gitea. The mail server was completely based on Postfix, Dovecot and the likes (Amavisd, Spamassassin, ClamAV). OpenLDAP was replaced by FreeIPA, StartSSL by letsencrypt. All this was setup via docker containers, for easier separation of services and for simpler management. Nginx was the reverse proxy. Besides the groupware components and the git server there was also a OwnCloud (later Nextcloud) instance. Some of the container images were upstream, some I built myself. There was even a secondary mail server for emergencies, though that one was always somewhat out of date in terms of configuration.
This all served me well for years. Well, more or less. It was never perfect and missed a lot of features. But most mail got through.
Why the restart?
If it all served me well, why did I have to re-create the setup? Well, a few days ago I had to run an update of the certificates (still manually at that time). Since I had to bring down the reverse proxy for it, I decided run a full update of the underlying OS and also of the docker images and to reboot the machine.
It went fine, came back up – but something was wrong. Postfix had problems accepting mails. The more I dug down, the deeper the rabbit hole got. Postfix simply didn’t answer after the “DATA” part in the SMTP communication anymore. Somehow I got that fixed – but then Dovecot didn’t accept the mails for unknown reasons, and bounced were created!
I debugged for hours. But every time I thought I had figured it out, another problem came up. At one point I realized that the underlying FreeIPA service had erratic restarts and I had no idea why.
After three or four days I still had no idea what was going on, why my system was behaving that bad. Even with a verified working configuration from backup things went randomly broken. I was not able to receive or send mails reliably. My three major suspects were:
- FreeIPA had a habit in the past to introduce new problems in new images – maybe this image was broken as well? But I wasn’t able to find overly obvious issues or reports.
- Docker was updated from an outdated version to something newer – and Docker never was a friend of CentOS firewall rules. Maybe the recent update screwed up my delicate network setup?
- Faulty RAM? Weird, hard to reproduce and changing errors of known-to-be-working setups can be the sign of faulty RAM. Maybe the hardware was done for.
I realized I had to make a decision: abandon my own mail hosting approaches (the more sensible option) – or get a new setup running fast.
Well – guess what I did?
Running your own mail server: there is a project for that!
I decided to re-create my setup. And this time I decided to not do it all by myself: Over the years I noticed that I was not the only person with the crazy idea to run their own mail server in containers. Others started entire projects around this with many contributors and additional tooling. I realized that I would loose little by using code from such existing projects, but would gain a lot: better tested code, more people to ask and discuss if problems arise, more features added by others, etc.
Two projects caught my interest over time, I followed them on Github for quite a while already: Mailu and mailcow. Indeed, my original plan was to migrate to one of them in the long term, like in 2021 or something, and maybe even hosted on Kubernetes or at least Podman. However, with the recent outage of my mail server I had to act quickly, and decided to go with a Docker based setup again.
Both projects mentioned above are basically built around Docker COmpose, Postfix, Dovecot, RSpamd and some custom admin tooling to make things easier. If you look closer they both have their advantages and special features, so if you think to run your own mail server I suggest you look into them yourself.
For me the final decision was to go with mailu: mailu does support Kubernetes and I wanted be prepared for a kube based future.
So with all this background you already know what to expect from the next posts: how to bring up mailu as a mail server, how to add Nextcloud and Gitea to the picture, and a few other gimmicks.
This will all be tailored to my needs – but I will try to keep it all as close to the defaults as possible. First to keep it simple but also to make this content reusable for others. I do hope that this will help others to start using their own setups or fine tuning what they already have.