Private messages shouldn't happen over the web - guess that nullified some of the points of running Mastodon.
My current email-form implies yes, the Indieweb approach implies no, whereas in the ActivityPub way, it's kept on both sides.
I found a spot in my room where I can hear my voice bouncing back from the walls with the right amount of delay that it is separate form the original. Fascinating!
Wash your hands! https://www.youtube.com/watch?v=Re0wYeK_rpU