I have used mailinabox.email (I think there is a docker version of it) and am quite happy with it.

I have a .yt domain, because it was cheap and had the three letter domain I wanted… I still dont understand, why that TLD ist more popular with youtubers…

I had problems with soft locks because somehow the PSU was in corrupt state, maybe through a black out or something. The problem persisted through reboots and power offs, only cutting power helped.