If you have already migrated from Lync 2013 on premises to Skype for Business on premises one of the features you can enable is the ability to search the Skype directory and federate with their users.
Here is a Technet article that goes into great depth for deploying Skype Connectivity with Public Providers for Skype for Business 2015: https://docs.microsoft.com/en-gb/skypeforbusiness/deploy/deploy-skype-connectivity?redirectedfrom=MSDN
If you had an environment that was already enabled for Public Providers, you only need to do the two following steps.
- Remove the Public Provider for Skype (or Messenger, or MSN)
- Remove-CsPublicProvider -Identity Skype
- Add a new Public Provider
- New-CsPublicProvider -Identity Skype -ProxyFqdn federation.messenger.msn.com -IconUrl https://images.edge.messenger.live.com/Messenger_16x16.png -NameDecorationRoutingDomain msn.com -NameDecorationExcludedDomainList “msn.com,outlook.com,live.com,hotmail.com” -VerificationLevel UseSourceVerification -Enabled $true -EnableSkypeIdRouting $true -EnableSkypeDirectorySearch $true
Now restart your Skype for Business client and you will see the Skype Directory search when you search a user.
Jacob Eker, PEI