Here some small informations in regard to XMPP.
Here you find a list of Providers where I think that they are good to go. There are some you may already heard of and who are often recommended and some more hidden ones.
To further advance decentralization I thought it may also make sense to mention some smaller projects.
I fished the providers mostly from compliance.conversation.im and one requirement was that the chat-service is available through IPv6. ;)
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