The creation of an XMPP federation for the "example.com" presence domain will be described step by step.
Start the estos UCServer administrator program and connect it with your estos UCServer.
Open the pages, Configuration -> Federation -> XMPP Federation.
Activate the XMPP federation by checking the Use XMPP Federation checkbox.
Select the Direct option from the options for connecting to other servers.
Set the TCP port to the default, 5269, by clicking the Default button.
Choose a server certificate. Without it, connection to other XMPP domains will not be encrypted using Transport Layer Security (TLS). See the Server Certificate section for more information.
Open the pages Configuration -> Federation -> Domain Authorization.
Click the "Add..." button, enter "example.com" for Domain Name on the subsequently appearing dialog or the name of the presence domain, to which you want to connect. Choose the desired presence authorization. Choose XMPP for Protocol. Select the desired type of encryption for the Encryption Type. The various types of encryption will be explained under domain authorizations. Complete the entries by clicking the OK button.
Click the Apply button to activate the settings just made.
If estos UCServer is in a private network connected with the public Internet through a router and firewall then, depending on the circumstance, it may be necessary to have the router and firewall forward port 5269 to estos UCServer. Precise information about this can be found in the documentation for the firewall and router. Make sure that the Windows® firewall running on the computer that is running estos UCServer is not blocking port 5269 and setup a corresponding rule, if necessary.
So that "example.com" can connect to estos UCServer, DNS must be able to resolve the name of the presence domain to a public IP address through which estos UCServer can be accessed. If such a DNS record does not yet exist, it should be created. As a rule, a DNS A Record will suffice, since external XMPP servers will attempt to access estos UCServer through the default port, 5269. If an external XMPP server does not support this, A DNS SRV Record will be required as will be described in the next step.
Creating a DNS SRV Record for XMPP Server-to-Server Connections:
A Service (SRV) Resource Record can be created on a Domain Name Server (DNS) for making IP-based services easier to find in a domain. Additional information about a service may be made available (such as the server running the service, priority and so forth).
Such a Service Resource Record can be created as follows:
_xmpp-server Service Location (SRV)  ucserver.domain.de.
|_xmpp-server||The name of the service through which it will be found on the DNS. The name must be _xmpp-server for XMPP Federation.|
|Service Location (SRV)||The type of record contained by these lines.|
|||The priority of the service so that different, similar records can be prioritized. Not in use.|
|||Emphasizes the entry. It is not used|
|||The port number through which the service provided is made available is specified here. The pre-defined Port 5269 generally applies for XMPP Federation in accordance with the XMPP standard.|
|ucserver.domain.com||The computer providing the service. XMPP Federation will expect to find the computer running UCServer.|
How and where the Service Resource Records are created for specific DNS servers can be found in the corresponding manufacturer's documentation.