I came across some strange errors recently with a customer where the setup was as follows Lync/SfB on premise due to Enterprise Voice but had Exchange Online. Whereas the issues being seen were the OWA IM client wouldn’t sign in, on mobile devices the buddy list would not show at all and the mobile client would struggle to resolve names when you received an instant message. Upon further digging this was due to the Unified Contact Store that Lync 2013/SfB 2015 and Exchange 2013/16 use and share.

Now the following is the statement of support-ability from Microsoft referenced here: https://support.microsoft.com/en-gb/kb/2614614#bookmark-more

Supported Lync/SfB Scenarios

*Supported only for Skype for Business Online users in the hybrid deployment.

Now from this you will notice that UCS is not supported when you have Lync/SfB on premise and Exchange Online. Now I should point out at this stage that the UCS store was introduced in Exchange 2013/16 so if you migrated or are running Exchange 2013/16 this will affect you.

To resolve this there are a couple of options available:

1. Disable the UCS store before you migrate to Exchange Online – As this will back up the contacts and you will not lose your buddy list. (I will discuss the commands later on)
2. Migrate the users back to on premise and then disable UCS and migrate the user back to Exchange Online
3. Force disabling the buddy list which will wipe out the contacts from the Lync/SfB Client, however if you have not re pointed your Exchange records to O365 this may allow the back of contacts – However in my scenario I was unable to test.

The PowerShell commands available to this are as follows:

1. To disable UCS for the user – Invoke-CsUcsRollback ahandyblog@test.com -force -verbose
2. To create a global policy to disable UCS the following command is available:
   1. Set-CsUserServicesPolicy -Identity global -UcsAllowed $False
3. To create a policy for individuals you can carry out the following:
   1. Create a policy – New-CsUserServicesPolicy -Identity “DisableUnifiedContactStore” -UcsAllowed $false
   2. Then assign the policy to a user – Grant-CsUserServicesPolicy -Identity “ahandyblog” -PolicyName “DisableUnifiedContactStore”
4. Alternatively you can block globally and allow some users to still user UCS if there mailbox is on premise which is as follows:
   1. Create a policy – New-CsUserServicesPolicy -Identity “EnableUnifiedContactStore” -UcsAllowed $true
   2. Then assign the policy to a user – Grant-CsUserServicesPolicy -Identity “ahandyblog” -PolicyName “EnabledUnifiedContactStore”

Once you have carried out the commands the mobile client and OWA IM should start to work immediately.