I've been running my self-hosted one user Pleroma (like Mastodon) instance. When I discovered Lemmy I started following some communities from it and also posted some comments.

Since then lemmy.ml makes one request per second to my /inbox url.

Can someone who knows ActivityPub explain why is necessary one request per second always? What are all these POST requests for?

On top of that, is there any way to tell a server or a relay to stop sending information to my inbox? Like if for example I followed someone in that server, but I don't follow them anymore, is there any way to tell the remote server to stop? If I start returning a 403 or something like that will it stop?