@heluecht @evan I'm also glad sharedInbox exists!
The issue I had with sharedInbox was that I was proposing that it should respect the actor model for delivery and we could do this by the posting server adding an HTTP header which listed all the intended recipients. However, Mastodon's devs said "no, we're already tracking the follow lists ourselves so we'd rather use our own information"
And I conceded to that at last minute because we needed to get the spec out. This lead to several issues!