RFC822 makes Spamassassin unhappy and I learned isn't actually compliant with revisions to the message spec!

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.

Yet! Decoding shouldn't be too hard. But for now it's a TODO. At least error out so we don't send out crazy messages.

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.

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

That is, delegate all message handling, incoming and outgoing to a short-lived process. Maybe this is really like sendmail but I dunno. Anyway it works and this is a big and bad enough commit already!

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!