The European Medicines Agency (EMA), which is the regulator for vaccines and medicine in the European Union (EU), has stopped using the social media platform X. The website is owned by Elon Musk, who is an important ally of the newly elected United States president Donald Trump. The EMA, whose headquarters are based in Amsterdam, is currently the only EU organization to leave the platform.
No, ActivityPub only send messages to the recipients. Uninvolved servers don’t get the message at all until one of their users explicitly searches for it.
In the worst case where every user has their own server, one message per recipient is sent. Adding another recipient on their own server means one more message being sent and so forth.