The federation between mastodon and lemmy is strange. If a M account wants to follow a L community, they need to follow an automated M account which represents the L community. But if any M post mentions that L community, the post will get boosted by the community’s M account, so everybody who follows will get a notification. And I’m not sure if this can be moderated from the L side, because it seems like it never goes through L. Such as - do you see this @opensource ? Does a L mod see this?
For those that are confused, realize Lemmy and Mastodon are two ways of displaying the same ActivityPub information:
Mastodon “favorite” is a Lemmy “upvote”
A Lemmy “comment” is a Mastodon “reply”
A Mastodon post with a mention is a Lemmy post within a community
A Lemmy “community” on Mastodon appears as a Mastodon account that boosts (retweets) everything that tags (is posted within) it.
Viewing a Lemmy community from Mastodon shows the entire community (posts and comments) in chronological order. Yes, it’s messy but doable.
Viewing a Lemmy account from Mastodon shows a feed of that user’s posts with URLs to the Lemmy instance they were posted to.
If a Mastodon user mentions a community, that toot gets posted to the community. Replies to the toot appear as comments on Lemmy and replies on Mastodon.
As others have noted, a toot exceeding a Lemmy instances character limit (200 I think by default) will be cut off on Lemmy and “overflow” into the “body” of the post.
Things that don’t directly “translate” AFAIK are the downvote arrow and the community moderator for both of which Mastodon has no equivalent.