Fail to log in account on web

Dear @Admin (Reef Systems),

Good day! Thank you for posting to Microsoft Q&A. We are happy to assist you!

Please understand that our forum is a public platform, and we will modify your question to cover your organization domain name in the description. Please notice to hide these personal or organization information next time you post error or some information to protect personal data.

First of all, we regret for the inconvenience caused to your work. Based on your description, it appears that your tenant has encountered an issue while attempting to access Outlook Web App (OWA). The TenantAccessBlockedException error usually indicates that your Microsoft 365 tenant has been blocked, often due to an expired subscription, billing issues, or specific policy violations. 

To understand the situation and be able to offer you relevant suggestions, we would need a little more information from you. Kindly help us in providing the following information. 

• Check Service Health: Go to the Microsoft 365 Admin Center and check the service health dashboard for any ongoing issues.
• Verify Tenant Status: Ensure your subscription is active and in good standing.
• May I double confirm that you checked with Admin if your account still has license? To check this kindly sing into https://admin.microsoft.com/ with Admin credentials > choose Active User under Users > click on your username--> choose Licenses and apps > Expand Apps > Make sure that Exchange Online (Plan1 or 2) is selected. If your account has license kindly uncheck it and reapply it, then wait the sync period to see if it will make any difference. 

If you don't have Admin privilege, kindly contact your organization Admin to check above for you. 

You may also refer to Getting a mailbox not found error in Outlook on the web - Microsoft 365 admin | Microsoft Learn. 

If the issue still persists, you may also (use admin account) to go to Office 365 Admin Center> Support > New Service Request. The support engineers there have the correct escalation channel, and this is the most efficient way to report such issue. You can refer to this article to check the way how to raise a ticket: Ways to contact support for business products - Admin help. The engineers in related team have higher permission and resources than us to help check the root cause from background directly. 

We look forward to your response. Kindly note that the above requested information is required for further analysis and troubleshooting of your situation.

Your patience and cooperation are much appreciated. Have a nice day! 

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