@Sylvester- I am not sure how the granular interaction works with the Federations.  There may even be more configuration options available through PowerShell or other API. To Be Honest.  We are not using Federations or Trusted Domains , Yet! One of the other problems is the speed at which changes are being made with the Teams platform / service. Just about the time I think I have a grasp of what is happening , they make more changes. 

Having said that, it seems that all parties involved in setting up Federation have responsibility for adjusting configuration options in their own Domains for things to work (or not). If you do start setting up Federations & Trusted Domains, I would make sure I have Global Admin contacts for all parties involved.  Sometimes the smallest change in the settings will have a large impact.

Another thing to be careful of is HOW LONG some changes take to become effective. If you read many of the posts on Teams configuration problems you will learn that sometimes it takes several hours for the change you make to actually become effective.

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