@nprofile1q... Private mentions aren't really private if they're not end-to-end encrypted. On a federated platform, you put a lot of trust on the servers, and it's not just the one you're on but also the one receiving the messages. What if I want to message a friend on Threads for instance? I don't know about you, but I don't trust Meta to just deliver the messages without using them to build a profile on me or improve their AI models, which are things I can't really opt out of since it's not my platform. The only way to avoid these things (to some extent) is to make it impossible for them to read my messages.

The good thing is you don't have to reinvent the wheel here, there are already a few attempts at standardizing encryted messages for ActivityPub: Evan put together the MLS over AP, Hollos also did something similar. Make sure to talk to them so we don't end up with yet another standard.