In the previous tutorial we have learned how to send a reply to another ActivityPub server, and we have used mostly static parts to do it. Now it’s time to talk about how to subscribe to other people and receive messages. The inbox Primarily this means having a publicly accessible inbox and validating HTTP signatures. Once that works, everything else is just semantics. Let’s use a Sinatra web server to implement the inbox.| Mastodon Blog
Translate `user@domain` mentions to actor profile URIs.| docs.joinmastodon.org