If a user can’t access your tenant and forwards the following message to you, here are the steps on how you can solve it.

Your account is blocked

We’ve detected suspicious activity on your account.

Sorry, the organization you are trying to access restricts at-risk users. Please contact your admin.

The unblock is done by either resetting the user password or clearing the user risk once you have assessed that the risk is resolved.

• If you have AAD Premium P2 (you can check it on the overview page of Azure AD), remediate the user risk by following this link Identity Protection | Risky users. A password reset is usually suggested and will also clear the user’s risk.
• If you do not have AAD Premium P2, you can reset the user’s password or let them do it by themselves by using Self Service Password Reset (SSPR) if you have configured it. Alternatively, you can also go on this page, and ignore the user risk, once you have assessed that everything is resolved: AAD Risky Users. All these methods will clear the user risk.

Allow 10 – 15 minutes before the user can access again without getting the error reported above.