Self hosting mail on a shared server in Moldova is basically the entire idea behind email (and the internet).

Which with cheap models like Jev as spam classifiers, this can now become a reality.

The problem is, Google and Microsoft have monopolized the entire email market, so their esoteric deliverability mysticism from 2007 still persists (basically blanket bans on entire IP spaces, locking out anybody trying to send emails on their own).

People used to have party lines and leave their doors unlocked too, but it turns out the world is filled with bad actors and other assorted shitty people.

Email naturally followed this evolution.