Teams federation between two 365 tenants

Allan Stark 1 Reputation point

We have two dedicated MS365 tenants. One of them has sync with on-prem local AD.
Once there was Exchange, but mailboxes were migrated a few years ago to the 365/ExO cloud and since then synchronization has been configured only for password hashes in both directions (not a hybrid).
Also no any SfB and never was in both tenants.
Users in both tenants have MS365BP and MS365E3 subscriptions.

I need to federate MS Teams between these 2 tenants, so that users can communicate in several Teams in both tenants.
I have followed all the recommendations described in this article:

All settings (except that Org-wide settings have been moved) have already been set by default.
I tried to create a new team in first tenant and add users from second tenant to it by their main email address / UPN, but it just doesn't find them.
The same and vice versa.
I tried to explicitly specify the allowed tenant domains in the External access settings in both Teams Admin Centers and even waited more than 24 hours. But with same result.
Team owners also cannot invite users from another tenant to their Teams.

After that I tried to add guest users in both tenants and after that these users can be added to teams and channels.
But this is very inconvenient for users, because in their Teams apps they have to switch to the second (guest) account in order to communicate with users of another 365 tenant.

We have more than 200 users in the first tenant and ~100 in second and more than half of them must communicate with each other in teams in another tenant...

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3 answers

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  1. JimmyYang-MSFT 50,356 Reputation points Microsoft Vendor

    @Allan Stark

    According to your description, it seems this problem is related to external access in Microsoft Teams. By default, external access is turned on in Teams, which means that your organization can communicate with all external domains. If you add blocked domains, all other domains will be allowed; and if you add allowed domains, all other domains will be blocked. So we recommend you check if you add the domains in the blocked domains.

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    1 person found this answer helpful.

  2. Mr Sb 356 Reputation points

    What you are looking for is only possible by using Azure AD B2B collaboration. It's too much to explain in a single post so I would recommend to read the following article:


    0 comments No comments

  3. Allan Stark 1 Reputation point

    Thanks to all who responded.
    One additional question.
    In both variants of inter-tenant Teams interaction (federation and guests), do we need to pre-add users as guests to both 365 tenants? Because in a scenario when there are several hundred users in each of the 365 tenants, this is quite time consuming.