@Minotaur @henfredemars @technology You are using an account on lemm.ee to reply to someone commenting from an account on infosec.pub in a community hosted on lemmy.world.
Those are all running Lemmy software, but I am replying from an account on social.goodanser.com, which is running Mastodon software.
That's federation. We're all using different service providers, sometimes even different software, but we can talk to each other because they speak the same protocol, called ActivityPub. Threads.net has announced plans to support ActivityPub and conducted some limited trials, which they're in the process of expanding. They claim they intend to support it fully, but only for users who opt in to it.
Servers can block, or "defederate from" other servers, and many have chosen to preemptively defederate from Threads.
@LibertyLizard @technology It always has. They both speak ActivityPub.
The UX can be awkward though. As an example, I had to add the community tag to this comment manually, as it won't federate to lemmy.world otherwise. That's because Mastodon doesn't push replies to every server with users participating in a thread, which I think is a design flaw.
To post to Lemmy from Mastodon, just tag a community. You can load any of the fediverse links shown in the default Lemmy web UI in a Mastodon search box and reply to them. You can also follow a community and receive every subsequent post and comment as a boost (this is a bad UX and I don't recommend it), as well as follow Lemmy users, which you can't do in Lemmy itself. You cannot vote on Lemmy posts/comments from Mastodon.
I find tagging an appropriate Lemmy community from my Mastodon posts to be a good experience. You'll see a few of those from my @zaktakespictures account in @birding, and from @zakreviews in @flashlight.
I'm pretty sure Lemmy won't make new toplevel posts out of this in those communities since it's a reply, but I'm going to check just to be sure.