Since last month I heard a number of complaints, About users that are invited to join a Microsoft Teams Team as a guest. When they are trying to login to the environment they receive a Office 365 pop message: “Sign in was Blocked. We’ve Detected something unusual about this sign-in.”
Note: There is no message about conditional access or anything else.
You start thinking this is something which is created by the Active Directory of the other party since they were invited. But that is not the real issue here. And all Microsoft Teams settings are correctly configured as well. So anybody could join and it is also not a license problem (1 user may invite 5 other users)
So what is the real issue here?
If you’re getting a message about your account being blocked because it’s been flagged as being risky you need to contact your home tenants admin and have them remove the “Risky user” using the Azure Portal :
Go to Azure Portal -> https://portal.azure.com
It seems Microsoft has recently enabled a policy that blocks all risky users from logging in.
I tried this solution at a number of clients and the issue was gone.
A note: please keep on checking if it is not a real risky user with some fraud logins.
If you have not done it yet I would really encourage you to enable Multifactor authentication(MFA) for all users.
And explain to your users why you want them to use MFA.