Would either Calckey or Misskey be a good fit for what you’re looking for?

If you’re viewing it from a mobile device, it won’t display.

The URL for mod mail gives me this: /message/compose?to=/r/math.

If you’re unable to find an answer, you could resort to modmail to see if you can get a message (canned or otherwise) about their plans.

Relative links seem to be the best way to accomplish what you’re looking to do. So, in your example, it’s /c/x@y.org.

Doing it live

Reference: https://lemmy.dbzer0.com/post/6063

Relative links seem like the best way to accomplish what you’re looking to do: https://lemmy.dbzer0.com/post/6063