XMPP addresses works the same as email addresses. They are broken up into three parts that look like this: firstname.lastname@example.org/resource
The ‘‘resource’’ is optional and is used to indicate a particular delivery point of an XMPP packet. This allows multiple logins to the same user account to be active (e.g. email@example.com/work, firstname.lastname@example.org/home).
As with email, each server maintains it’'s own users accounts, determines their essential behavior (setting limits on what can be sent/received, etc).
When you add a user to the roster, you indicate the user to add by their full address: email@example.com (without the resource). For messenger users, if your messenger server domain is set to ‘‘server.com’’ and you can communicate with any other user with an account on the same domain (’‘server.com’’). Messenger currently does not support server-to-server (s2s) communication so you are only able to communicate with users on the same server. So for example, you cannot add ‘‘firstname.lastname@example.org’’ to your roster because the server is not the same.
Try to create two user accounts on Messenger, note their address (username@servername) then use Psi to add the users to each other’‘s roster. XMPP will require confirmation for the subscription so you should see the psi clients pop up messages asking you whether it should allow the subscription. if you respond with ‘‘yes’’ you’‘ll see the rosters with presence indications for the users. When a user logs on/off, you’'ll see their presence change.
We plan on adding s2s support to Messenger soon. Most of our customers so far run Messenger for internal, or closed user communities so s2s hasn’'t been that high a priority.