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Microsoft Teams CoExistence & Interop With Skype for Business

If you are thinking of introducing Microsoft Teams into your organization and you are currently using Skype for Business, then you will undoubtedly be wondering how these two distinctly different but similar apps interact. In this post, I hope to take a simpler approach to the Microsoft article to help explain the supported scenarios and where you may trip up if not careful.

Interop and coexistence when you have are 100% Skype for Business Online is pretty well established now and as long as you follow the rules of engagement, there shouldn’t be any issues. However, if you have an on-premises Lync or Skype for Business deployment, then things are a little more complicated if you want the users to use Teams as well.

Technically speaking right now, if your user is homed on-premises Skype for Business and is using Teams, this is not currently a supported scenario, although it may work to some degree, the likelihood of weird things happening is high. This is a scenario that will become supported in the near future though, so watch out!

There are a few things you need to do in order to get interop working between a Teams user and a Skype for Business on-premises user. First of all and most important, you must have Azure AD Connect deployed and syncing accounts to AzureAD. Within that sync you must make sure that you are syncing the attribute msRTCSIP-DeploymentLocator. This is so Skype for Business Online can properly detect your on-premises deployment.

Secondly, you must configure your Skype for Business on-premises deployment for hybrid with Skype for Business Online.


In fact, even if you as an organization are not moving to Teams and sticking with Skype for Business On-Premises, you must configure this if you want to continue to federate with partner organizations who are moving to Microsoft Teams!!

Now if you want to allow your users to use Microsoft Teams, you must first move them from your Skype for Business On-Premises to Online if your intention is to move them completely to Microsoft Teams. This will shorten in an upcoming CU for SfB 2015.

With hybrid configured your on-premises homed users can use Microsoft Teams in Islands mode, but will not be able to use Microsoft Teams to federate with external users, they must continue to use Skype for Business for that.  Furthermore they can only use Microsoft Teams to chat and call other internal users who are also using Microsoft Teams in islands or Teams only mode. They cannot use Teams to IM a Skype for Business internal user, they must continue to use Skype for Business for that.

A further note on federation, regardless of on-prem or online if the Teams user initiates a federated chat or call and the partner is in islands mode, the chat and call land in the partner’s SfB client, not Teams!

Skype for Business on-premises users cannot use Microsoft Teams for any phone system features, including direct routing or calling plans as they must be in Teams Only mode for these features.

However, Skype for Business on-premises users can use the Microsoft Teams Meeting features and Dial-in Conferencing should they wish (coming soon). Even though Microsoft say this is a Server 2019 feature, there is no dependency for on-premises software version for this to work.

To try and put this together as a quick reference I have put together the flows as a picture below

Hope this helps to keep clarity when working out what should and shouldn’t happen.




  1. Hi

    Very valuable Information – thank you!
    Is there any difference for a user in the coexistence Scenario in hybrid mode if an sfb user is online or on-premise?

    best regards – Urs

  2. […] Step 2 – Get out of Islands mode!You’ve probably downloaded teams and had a play, but if you want to mass adopt Teams in the organisation, Islands is not a long term Coexistence or Interop mode, it just doesn’t play nice when you start moving users from SfB to Teams Only mode. A lot of customers don’t even know they are in Islands! Further reading:https://regarding365.com/beware-of-the-island-understanding-teams-and-skype-coexistence-modes-300bcf412fa2https://erwinbierens.com/post/2019-04-18-get-the-hell-out-of-islandsmode/ https://blog.valeconsulting.co.uk/2018/10/26/microsoft-teams-coexistence-interop-with-skype-for-busi… […]

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