i found the error by myself. IMHO this is a bug within jabberd2 not responding to openssl s_client calls while using the FQDN instead of the domain part of the JID. especially because some xmpp clients give you the ability to connect to another host instead of your domain part of your JID.
I wouldn't say it's a bug. You didn't show us the complete configuration file, but I am assuming you did not configure jabberd2 to also serve xmpp.guuk.eu, so when you try to connect to xmpp.guuk.eu jabberd2 doesn't know that it should also serve users for x...@xmpp.guuk.eu. If you need that
so, i checked my configuration, but i am stuck, no ideas anymore what is missing or wrong. that's the software i am using. jabberd2 from unstable and openssl from testing (debian) # dpkg --list jabberd2 openssl Desired=Unknown/Install/Remove/Purge/Hold |