Did you know that you can follow the #XMPP group on Lemmy (federated forums/Reddit) directly from Mastodon? Check it out! https://lemmy.ml/c/xmpp
@brie My (limited) understanding is that most servers don't download old posts from servers they weren't previously federated with to save space. Once you add a new server though, new posts should start showing up!
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.