configuring external domain

My ejabberd server is reachable under jabber.example.com. I would like to use the JID name@example.com instead of name@jabber.example.com. I found a description how to configure my DNS defining SRV for _jabber._tcp.example.com _xmpp-server._tcp.example.com and _xmpp-client._tcp.example.com at https://ssl.tiggerswelt.net/wiki/jabber/externe_domains (German). When register a new user name@example.com at ejabberd I receive an error that this is not allowed. How do I have to configure ejabberd appropriately?

PS: I am using ejabberd 1.1.2 under Debian.