It's a different thing. E-mail, Matrix, and ActivityPub are all different protocols. Mastodon and Lemmy both exist on the ActivityPub (i.e., the Fediverse).
@Ghast
I'm not sure if that is a question or not, but in case it is —
Yes, that is correct.
Mastodon is the best way to keep up with what's happening.
Follow anyone across the fediverse and see it all in chronological order. No algorithms, ads, or clickbait in sight.