zsoltsandor, You still use email, right? That's how users in the #Fediverse are addressed with an extra @ at the front. But if you are capable of #email addressing, you can do user addressing on #Mastodon #Pixelfed #PeerTube #Misskey #Pleroma #Funkwhale #BookWyrm #Owncast #Castopod #Microblog #WriteFreely #Plume #Lemmy #kbin #mobilizon etc.
It's always @user - the simple magic of #ActivityPub.