I run this on a few small sites (e.g. https://tommasoamici.com) and it’s very cool that people can fully know what you’re tracking and eventually delete all the data you have on their own. The developers are also very open to feedback and suggestions. I highly recommend it!

I see no one has mentioned Mailu (https://mailu.io/1.7/). It’s a self hosted mail server made up of a couple docker images.

I would recommend it based on my use and experience.

I’ve been using it for my personal email and for automated no-reply messages in a few projects with no delivery issues. I’m hosting on a Contabo VPS.

It handles spam with rspamd, sets you up with DMARC, DKIM, has an admin interface, web mail interface.

What keeps me from running my own like this is stuff like, how easy would migration to another sever be and how easy is backup and recover.

Docker is pretty portable by design. If you use bind mounts you can just scp the docker-conpose.yml and your bind mount volumes to your new server and you're done. If using Docker-managed volumes you'll need to docker cp the data out of them first before scp, then docker cp them into your volumes once you docker-compose up your containers.

Seconded, I've used it for a couple of years and it's a great package that I find quite understandable (a docker-compose stack).