Server Error 500

Question

Hey, the following error popped up on outlook

UTC Date: 2026-06-02T20:55:38.344Z
Client Id: [Moderator note: Personally Identifiable Information removed]
Session Id: [Moderator note: Personally Identifiable Information removed]
Client Version: 20260522011.09
BootResult: throttle
Back Filled Errors: Unhandled Rejection: Error: 500:undefined|undefined:undefined
err: Microsoft.Exchange.Data.Storage.TooManyObjectsOpenedException
esrc: StartupData
et: ServerError
estack: Error: 500
    
    at [Moderator note: Personally Identifiable Information removed]
st: 500
ehk: X-OWA-Error
efe: v6
ewsver: 15.21.71.15
reqid: [Moderator note: Personally Identifiable Information removed]
cv: [Moderator note: Personally Identifiable Information removed]

Answer 1

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Hi @Dawson Simpson, 

I hope you are doing well today.  

Based on the information you shared that  you are experiencing a Server Error 500 in Outlook, triggered by a Microsoft.Exchange.Data.Storage.TooManyObjectsOpenedException error. 

This error occurs when the Exchange server reaches its limit on the number of simultaneously open objects within a single session, which can happen when Outlook is managing a large volume of emails, folders, or background sync processes at once. This typically affects accounts with a high mailbox load or when multiple sessions are running concurrently without being properly closed. 

At this stage, the issue cannot be resolved by an end user and requires assistance from an administrator. I kindly recommend contacting your IT administrator and asking them to confirm and reach out to them follow the steps below:  

• Ensure that your account has a valid Microsoft 365 license that includes Exchange Online (for example: Microsoft 365 Business Standard, E3, or E5).   

In the Microsoft 365 admin center, go to Users > Active users > [Your account] > Licenses and apps and verify that Exchange Online is enabled.   

1/ Ask the Exchange admin to check the server error logs 

• This error can happen when the mailbox opens too many items, folders, or connections at the same time on the Exchange server.  
• The Exchange admin can check Event Viewer for MSExchangeIS Event ID 9646, and also review 9660, 9667, and 9760, to confirm which mailbox or connection is causing the issue.  

2/ Ask the Exchange admin to check which mailbox is using too many resources 

• The Exchange admin can run Get-StoreUsageStatistics to find out whether one mailbox is opening an unusually high number of objects.  
• They can also run Get-MailboxStatistics to see whether the mailbox has folders with a very large number of items, because large folders can increase server load when Outlook on the web starts 

If Exchange Online is not enabled, the correct license should be assigned. In some cases, removing and then reassigning the license can help reactivate the service, although this process may take up to 24 hours to fully apply.  

If your IT team confirms everything is in order and the issue persists, they may need to escalate the case to Microsoft Support through the Microsoft 365 Admin Center for further investigation.   

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn    

In case you do not know who is your IT admin, kindly refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support  

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.         

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.           

Thank you for your patience and your understanding. I look forward to continuing the conversation. 

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Answer 2

The error indicates an HTTP 500 server error in Outlook on the web caused by a backend Exchange exception (Microsoft.Exchange.Data.Storage.TooManyObjectsOpenedException). This is a server-side issue, not a client configuration problem.

Actionable steps:

1. Wait and retry
   • Similar 500-level issues in Outlook/OWA and Microsoft 365 services can be transient. In a comparable case, the issue cleared after about 30 minutes and sign-in started working again.
   • Sign out of Outlook on the web, close the browser, then sign back in after some time.
2. Reduce server load patterns (if possible)
   • Avoid rapidly opening many folders, messages, or performing bulk operations in OWA for a while, as the exception name suggests too many objects are being opened on the server side.
3. Check service health / contact admin
   • If using a work or school account, the tenant admin should check the Microsoft 365 Service Health dashboard for any ongoing Outlook/Exchange incidents.
   • If the issue persists across multiple sessions and devices, the admin should open a support case with Microsoft, providing:
     • UTC time of failure
     • reqid, cv, and Client Version from the error
     • The exception name Microsoft.Exchange.Data.Storage.TooManyObjectsOpenedException and HTTP 500 details
4. Try alternative clients temporarily
   • Use Outlook desktop or Outlook mobile (if available) to access mail while the web issue is investigated.

This scenario is a server-side condition; resolution typically requires either waiting for the transient condition to clear or admin/Microsoft intervention rather than local troubleshooting.

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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