XMPP doesn't need "sealed senders", because it's not a centralized services to begin with.
Good feature sets?
XMPP and all the software around it is well maintained as well. It's also supported AND used by many well known companies.
It's also a lot easier to use. It's also not exclusive in any way. You can use it however you want to use it.
Servidor social en català per a la comunitat de llengua i cultura catalanes d'arreu d'internet.