I have received this error when trying to access Outlook on Enterprise licence of 365.

Question

I have received this error when trying to access Outlook on Enterprise licence of 365. Can someone tell me what it means? and how to fix it. Thank you!

UTC Date: 2026-03-25T09:28:08.079Z
BootResult: configuration
Back Filled Errors: Unhandled Rejection: Error: 500:undefined|undefined:undefined
err: Microsoft.Exchange.Data.Storage.TenantAccessBlockedException
esrc: StartupData
et: ServerError
estack: Error: 500
st: 500
ehk: X-OWA-Error
emsg: TenantAccessBlockedError

[Moderator note: Some personal information has been moved to private message]

Answer 1

Hello @Rebecca Hollands,  

Good day! I hope you're doing well.

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This error usually occurs when an account doesn't have an active Exchange Online license. You can verify this by following these steps:

• Sign in to Microsoft 365 Admin Center using an admin account. If you don’t have admin privileges, please contact your organization’s administrator to perform the steps above. 
• Go to Users > Active Users 
• Click on your username 
• Select Licenses and Apps 
• Expand Apps 
• Ensure that Exchange Online (Plan 1 or Plan 2) is selected 

If the license is present, try unchecking it, reapplying it, and then allow some time for synchronization. This may help resolve the issue. 

You may find this article helpful: Getting a mailbox not found error in Outlook on the web - Microsoft 365 admin | Microsoft Learn. 

 

If the issue persists, please ask your admin to confirm if the subscription that includes Exchange Online Plan is still active.

If it is still active, I recommend submitting a support request to Microsoft Technical Support Team. They can help verify your account license and perform deeper troubleshooting with their advanced tools:

• Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn    
• If your organization's Office 365 Business/Education subscription is from a partner or reseller, and the global administrator is unable to open a service request on your end, contact the reseller's support provider to help open a service request on behalf of you instead.    

I hope this will help. Please feel free to reply if you need any further assistance.

I'm looking forward to your response.

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Answer 2

The error Microsoft.Exchange.Data.Storage.TenantAccessBlockedException / TenantAccessBlockedError means that access to the Exchange Online tenant is currently blocked at the service level. When this happens, Outlook on the web (and often other Microsoft 365 services like Teams or Outlook desktop) cannot access mailbox data and return HTTP 500 errors.

This is not a client-side configuration issue; it is a tenant/service issue in Microsoft 365.

Resolution steps:

1. Contact the Microsoft 365 administrator for the organization.
2. The admin should sign in to the Microsoft 365 admin center and check the following:
   • Service health for Exchange Online and related services.
   • Any notifications about the tenant being blocked or restricted (for example, billing, compliance, or security-related holds).
3. If no clear cause is visible, the admin must open a support ticket from the Microsoft 365 Admin portal so Microsoft support can investigate and remove or remediate the tenant block.
4. While the tenant is blocked, use alternative access only if available (for example, if some accounts are still working), but in most cases Outlook on the web and Exchange access will remain unavailable until Microsoft clears the block.

A similar tenant-side issue described in the context (TenantAccessBlockedError in Outlook/Teams) was resolved only after waiting for the service condition to clear or after Microsoft support intervention.

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References:

• Tried loggin into Teams and Outlook and got this message on outlook, and unable to log into teams. - Microsoft Q&A