When we receive activity that has a collection, we see if any of the other actor recipients have the collection set as their followers. Then we can encode it with plus addressing. If we can't do that we drop it. Not ideal, but it covers most use cases. Next up we can encode arbitrary collections like "some/path/to/thing@example.com".

The receiving server can forward the message for us. For us to resolve the entire collection is a lot of work, especially since paginated followers collections only contain like 12 entries per page! Lots of people have over 300 followers.

Moved to package sys, generated dynamically (and tested!).

We've already looked up the entire actor so may as well return it, then let callers do what they want with the data.

I made a bit of an announcement to fediverse@lemmy.world: https://old.lemmy.world/post/12791602 Replies were delivered ok to my ActivityPub inbox and my mail inbox. And I replied to those from my email client, too!