We had a customer recently report an issue, where they were able to federate with one of their suppliers. If they were set to open federation presence showed correctly and communication worked fine. However as soon as the customer changed to closed federation they were getting presence unknown.
We confirmed they added the customer as a SIP federated domain and provided the Access Edge service configuration which they had done.
So, we then focused on the Edge server logs and found the below error referencing the domain were having issues federation with.
This error typically occurs when the Access Edge service configuration specified in the Skype Control Panel for the federated domain is incorrect. As we knew that open federation worked with no issues and that relies on getting the access edge address manually from the following SRV Record _sipfederationtls._tcp.FEDERATIONPARTNERDOMAIN.com we decided to see what that DNS record referenced.
You can do this easily by opening a command prompt and running
nslookup -q=SRV _sipfederationtls._tcp. FEDERATIONPARTNERDOMAIN.com (Change FEDERATIONPARTNERDOMAIN to the domain you are federating with)
This gave us the following output:
As you can see this references Skype Online, so we compared this to what the customer had provided as the access edge server for who they were federation to. We changed this to sipfed.online.lync.com and federation started working straight away!