Hi @IBN
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According to your description, it contains two questions. As we mainly focus one question in each thread. For outlook question, we recommend you post another thread to the forum and add outlook tag. Thanks for your understanding and patience!
For Teams client, could you find the error message or code when sign in Teams? If you can see it, please share it with us.
Can they login in Teams web client normally? If the answer is yes, then you could try to clear your Teams client cache file and restart by following these steps:
1.Holding the Windows key, press R to open Windows Run, then copy and paste the following into the box and click OK:
%appdata%\Microsoft
2.Find the Teams folder, then right click it and select Delete
3.Relaunch Microsoft Teams.
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