@evan @davew this is similar to one approach to support reply controls: Every response to a post goes first to the OP's device (or trusted server), which can then apply any configured reply controls, and then forward it to the original post's recipient list (or a subset) as appropriate. This also has the advantage that a replier can remain anonymous to other recipients, while not anonymous to the OP, which I think would help discourage anonymous abuse. I've implemented this in a social media system I wrote.

The OP's device could even avoid sending these replies to people blocked by the replier, by using private set intersection (PSI). Updatable PSI would make this efficient.

I think reply controls would go a long way towards attracting people to the fediverse who face a lot of abuse online.