You make a good point, especially around isolation. While I use docker and I know the basics of it, I'd hate to try and debug it if something went wrong (i.e. postfix container wouldn't start). For that reason I've stayed clear of using it for "critical" life things, like our email. For a number of years there my wife's business email I was also sending through my mailserver, so it needed to be super reliable. I'm not saying docker/mailcow isn't reliable, only that if it did break in funky ways, I don't have the knowledge domain to fix it. But I'm familiar with all the individual programs and running them on a "flat" linux system, so that's what I did. But yes, you certainly make some good points that are worth considering if someone else is reading these comments and thinking about doing it themselves!