The estos UCServer needs an unequivocal address for every user for presence and Chat, the so-called "identity". The identity is composed from the username and the presence domain.
A presence domain is distinctly and permanently assigned to a estos UCServer. The estos UCServer is responsible for the transmission of the presence information of all users. This can be done, if required, via Federation also accross the company boundaries.
The same presence domain may never be used on multiple servers. The presence domain must not be changed anymore. Please note that with an alteration to the presence domain all users on the server are no longer accessible to external contacts, because the user's identities change with the presence domain.
The presence domain can be exclusively changed via the server setup, i.e. by a new installation, upgrade or update. Please note that by updating the presence domain all user profiles on the server are customized. Similarly, Setup will try to update all of the favorites and monitor content of workplace software to the changed user identities. After the upgrade, you will be prompted to check the user profiles, especially the user identities.
Ideally, the identity of each user should correspond with their e-mail address. This is important if you want to exchange your presence information and chat messages with external users beyond the boundaries of the enterprise network. The estos UCServer can enable communication with external users via the e-mail address. To ensure that the identity and the e-mail address fit together, you should use the same presence domain for your e-mail addresses.