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Russ DillionFlag for United States of America

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How to achieve inter tenant \ domain use of MS Teams and Skype

Hello Experts,

I support multiple companies and am working to enable inter domain \ inter tenant use of Teams and Skype between some of them per the article listed at the url below.  Currently, I've made changes in the Microsoft Teams & Skype for Business Admin Center --> Org-wide settings --> External access area for each of the three, enabling "External access" and "Users can communicate with external Skype users" and then adding the other two domain names with status of Allowed.  After doing that I had some initial success in chatting with a user in one of the other domains when logged into the Teams app on my local system.  Since that time, however, I have attempted to chat with other users in the two other domains from my Teams app, with no success.  When I send a chat message, I typically get a message stating "This user is unavailable or offline.  We've sent an email instead.".  I even observed this when sending a chat message to another user, when I was connected remotely to his system, and was able to verify he was logged into the Team app on his system.  Is there anything else from a configuration standpoint that I need to complete?  Do I need to enable Guest access in Teams for each of the tenants?

Thanks in advance,


Microsoft 365Skype

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Albert Widjaja
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Vasil Michev (MVP)
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External/federated communication in Teams is a mess, despite what Microsoft's marketing team is trying to tell you. Use Skype for Business where possible, or grind your teeth for few more months until they solve the issues :)

On the bright side, meetings mostly work.
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Albert Widjaja
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There is this article already for Configuring Office 365 Microsoft Teams and Skype for Business Federation.


Hope this helps.
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Russ Dillion
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Thanks very much for the link to that article.  I'll take a look and see if I can make any more progress.
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Russ Dillion
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I ultimately engaged MS support on this, and the only way they were able to accomplish what we were looking for was to do the following on all of our participating tenants:

In Office 365 Admin portal go to Teams admin center -> Org-wide settings -> Teams upgrade and change the Coexistence mode to Teams Only (default was Islands).  After doing this our users were able to chat between our tenants using Teams
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Russ Dillion
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Hi Russ,

Thanks for sharing.

So now your user, can invite anyone they know to the Teams Channel?
Microsoft 365
Microsoft 365

Office 365 is a group of software plus services subscriptions that provides productivity software and related services to its subscribers. Office 365 allows the use of Microsoft Office apps on Windows and OS X, provides storage space on Microsoft's cloud storage service OneDrive, and grants 60 Skype minutes per month. Office 365 includes e-mail and social networking services through hosted versions of Exchange Server, Skype for Business Server, SharePoint and Office Online, integration with Yammer, as well as access to the Office software. All of Office 365's components can be managed and configured through an online portal; users can be added manually, imported from a CSV file, or Office 365 can be set up for single sign-on with a local Active Directory using Active Directory Federation Services.

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