Unable to federate with Office 365 Lync Online

In a Lync On-premise deployment, you may find yourself unable to federate with users in a Office 365 Lync Online domain even though you both have Open Federation set. The remote user appears as “Presence Unknown” in the Lync client and the following error can be seen in the UCCAPILOG log:

Unable to Federate – SIP/2.0 504 Server time-out 1009;reason="No match for domain in DNS SRV


Add a new hosting provider for Lync online by running the following in the Lync Management Shell:

New-CSHostingProvider –identity LyncOnline –ProxyFqdn sipfed.online.lync.com –Enabled $True

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