IMAP is the protocol you probably want.
I’m quite happy with “Mail In A Box” as a platform for hosting mail locally with clients.
There are companies that will do inbound spam filtering and outbound mail relaying to ensure high reputation for outgoing main also. I have clients on duocircle but they’re grandfathered in on reasonably priced plans (the new plans are probably a little expensive for self hosted home mail)




Here’s a hot tip: get some DIY tea bags for a few bucks on Amazon (or your preferred cheap tat bazaar)…
I make my own dessicsnt packs for use with 3d printer filament spools when I store them, and the tea bags are a godsend.