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".

Clearer: set a body to read from, then change it when necessary. Fewer instructions! Also, mail clients don't really know what to do with text/markdown, so just use text/plain; that's what Gruber would want. Adds basic test case too

This seems clear enough. In the regular email world we want direct recipients to be signalled in some way of our message. Recipients merely copied in (CC'd) don't need to be alerted but still get the message.

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!