Microsoft Teams Admin Center

Browse to https://admin.teams.microsoft.com.

<User>@tbhf.onmicrosoft.com
bhf-it@bhf-th.org

Click Next.

********

Click Sign in.

Uncheck Don’t show this again.

Click No.

Do your thing.

Select Account manager > Sign out.

Close Browser.

Select Users > External access.

Select Allow all external domains for Choose which external domains your users have access to.

Turn off People in my organization can communicate with Teams users whose accounts aren’t managed by an organization.

Turn on Allow users in my organization to communicate with Skype users.

Teams and Skype for Business users in external organizations
  Choose which external domains your users have access to:
    Allow all external domains

Teams accounts not managed by an organization
  People in my organization can communicate with Teams users whose accounts aren't managed by an organization
    - Off

Skype users
  Allow users in my organization to communicate with Skype users
    + On

Click Save.