Microsoft Teams to allow external user communication

November 11, 2021


  • On Tuesday, November 30, 2021, Microsoft Teams will be modified by ITS to allow external user communication.
  • You will be able to call, chat, and set up meetings with people external to the University who use Microsoft Teams or Skype for Business and are also using open communication OR that has added Yale’s domain to their allow list.
  • Reminder: It is the responsibility of the data owner or anyone with access to it to only share sensitive data with appropriate audiences. Please review the Yale University Microsoft 365 Terms and Conditions for Storing Sensitive Data.


What do external users need to do to communicate within our environment?
External users can use open communication, or they will need to add the domain to their allowed list to become a federated user.

How do I know when I am chatting with an external user?
You can easily see when you are chatting with a person external to Yale University; below their display name in the chat, you will see their organization’s domain name (e.g., In addition, to the left of the video call and audio call buttons, you will see a tag that says External.

Can I block an external user from communicating with me?
If you receive a chat from an external user that you do not want communications from, you can right-click the chat message and select the Mute and Hide options from the popup menu to prevent you from seeing any further messages from them.

What can a federated user do?

  • Chat with users within our environment
  • View files shared with them in chat messages
  • The following specific features are only allowed if the external user’s organization is in Teams Only mode:
    • Share their screen
    • Edit or delete sent messages
    • Use Giphy, memes, and stickers

What can’t a federated user do?

  • Search the user directory; they must know your email address and enter it directly.
  • Share files
  • Access Teams and Channel resources. This involves inviting the person as a guest to your team. See below for further information on guest access.

How does guest access differ from external user access?
Guest access is where the collaboration happens. Guests get access to the teams, channels you’ve invited them to, as well as files and discussions shared within those channels. Guests can search for people (limited to people within the Teams they have access to), guests can share files (limited to sharing within the Teams they are members of). Whereas external access user is outside looking to talk, your guest access users are someone you’ve invited into our environment.

Have a Team supporting a customer project? Guest access can enable those customers to view the project collaboration. Have a Team for vendor collaboration? Guest access can enable that vendor to view the conversations and files.

What guests can do is a long list, so let’s focus on what they CANNOT do (complete list here):

  • Cannot share a file in 1:1 chat.
  • Cannot search our Global Address List for users in our organization; they can ONLY search for members of Teams they are members of.
  • Do not have a calendar and cannot access scheduled meetings or meeting details unless they receive an invitation to it at their email address.
  • Cannot create a Team or change an existing one.
  • Cannot browse for Teams to join.


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