Auto-populate IM Roster
Within the <domain> Services tab, you can tick the Instant Messaging shared roster (Populate with all domain users) box. In this case, the <install_dir>/config/<domain>/roster.dat file is created with the domain name added. This populates IM rosters with domain users names without necessity to authorize each other.
It is possible to add a group (or more) to this file. Use a single line for each group with the following syntax: [group_name]. You can even delete the domain.