well gmail does the same. At least with username@facebook.com, you could contact friends on facebook without actually logging into facebook. Actually I'd like

well gmail does the same. At least with username@facebook.com, you could contact friends on facebook without actually logging into facebook. Actually I'd like more social networks to be "federated" like that. ActivityPub is one such protocol, whereby users on different networks like Mastodon and PeerTube can communicate.