my eJabberd server is now up and running and I can receive messages and send messages.
My next step is to setup the chat functionality in roundcubemail so you can send messages through a Jabber client or roundcubemail. :-)
I had to find the correct settings for my domain and the client to get it to work. So it's necessary to have proper DNS records for your domain and the services jabber is running on.
You must have a A/CNAME record for your domain (no wildcard, -> "nslookup domain.com" should work) and 3 SRV records for your domain where you setup your jabber server where all the clients and servers have to connect to.
Also you should use SASL for authentication purpose.
I prefer to have my domain as the jabber ID and not a subdomain.