I've tried mailcow, and it is also being considered. I'm trying to dig up "dirt" on it to see just how secure it is.

I'm always very nervous when it comes to running docker in production. Also, it looks like it (by default) stores emails in a docker container, which in my book is just overcomplicating things. While i don't mind software being containerized, i much prefer having my data stored in the plain old filesystem.