(Not only) Because the biggest XMPP-compliant server (talk.google.com), which doesn't use server to server encryption, seems to leave the XMPP federated network (GTalk -> Hangouts), we want to make the XMPP network more secure:

This year, 2014, we'll require on some test days to connect other servers only encrypted to ours. If you've problems on these days to reach some of your contacts from other Jabber/XMPP servers, please contact us, or even better: the admin of the other Jabber/XMPP server.

The schedule:

January 4, 2014 - first test day requiring encryption

February 22, 2014 - second test day

March 22, 2014 - third test day

April 19, 2014 - fourth test day

May 19, 2014 - permanent upgrade to encrypted network

Update April, 18: because too much problems with encrypted server2server connections we will still prefer and recommend encryption, but not disable unencrypted connections.

Update May, 19: As the self-signed certificate for 0nl1ne.at seems to be working (the CaCert one was too modern signed for some other servers) we switch today to required server-to-server communication.

More information will follow and can be found here (XMPP Manifest).