/etc/jabberd/c2s.xml and change the content of the tag
<id register-enable='mu'> to your domain.
That is the line that will be added to your users id. (If you put there
example.com, your users id will be something like
If the jabber service is going to be accessible over open internet (instead of a VPN or LAN), then that name SHOULD be resolved by DNS to your server.
register-enable='mu' part, allows the registration of accounts, using a standard jabber client.
Also set your server on
jabberd.service to start on boot.
Read Daemons for more information.