Preface this with the fact that we are a onmicrosoft.com tenant and don’t have Exchange setup in Office 365.
We can’t @ a user to chat without initiating the chat first in the Teams User Profile under Teams admin. Once we initiate the chat by clicking on the icon on the Teams Admin Portal and it are asked to open within the Teams app, the user can be @ to chats. BUT only by the person that has done the steps above. This process needs to be done by each person that needs to see the user in Teams.
Does this make sense? I couldn’t figure out a better way to describe the issue.
Thank you!
