Error 500 and Error X- OWA - Error

Question

I am having an erorr X-OWA and 500. Its been days and I followed some steps regarding billing products and licenses and its in active status but still having an error. Anything I need to do?

Thank you

Answer 1

Dear @gisselle,

Thank you for posting your question in the Microsoft Q&A forum.

I apologize for any inconvenience you may encounter when using our services/ products. Based on your description, kindly try these following steps:

If you are an end-user: Please contact your IT Administrator for further assistance. How do I find my Microsoft 365 admin? - Microsoft Support

If you are a Global Administrator of your tenant:

Check your Exchange license

• Go to Microsoft 365 admin center > Active Users > [Your account] > Licenses and apps
• Make sure the Exchange license is assigned to your account.

Use InPrivate/Incognito or a different browser

• Try InPrivate/Incognito in a browser, or a different browser to sign in to OWA.
• If this works in InPrivate, the issue is often tied to cookies/session state (clearing site data for Outlook can help).

As a moderator, I do not have the tools to investigate your specific account directly, as this is a support forum between users. Moderators and collaborators, including external Microsoft employees, may not directly intervene in the functionality of Microsoft products or access internal systems. Our role is limited to providing technical guidance on reported problems, requests, or ideas. However, I will do my best to guide you as clearly as possible.

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Answer 2

Error 500 and X-OWA issues are typically server-side problems in Exchange/Outlook on the web (OWA), not billing or licensing problems, especially if the subscription is already confirmed as active.

Based on the available information, the following server-side causes and fixes are documented:

1. Malformed OWA requests causing HTTP 500 (OwaSerializationException)
   In Exchange Server 2013/2016, a malformed JSON request in X-OWA-UrlPostData can trigger HTTP 500 with OwaSerializationException. This is a known product issue and a potential vulnerability.
   The documented fix is to update Exchange to a sufficiently recent Cumulative Update (CU):
   • For Exchange Server 2013: install Cumulative Update 14 or a later CU.
   • For Exchange Server 2016: install Cumulative Update 3 or a later CU.
2. HTTP 500 after Exchange updates (Outlook on the web / ECP)
   If HTTP 500 started after installing a security update or CU on Exchange, and errors mention missing assemblies such as Microsoft.Exchange.Common, the documented fix is to reinstall the security update from an elevated Command Prompt and then restart the server.
3. HTTP 500 in EAC due to admin/arbitration mailbox issues
   If the error appears when signing in to Exchange Admin Center (EAC), and logs show OrganizationMailboxNotFound, the fix is to:
   • Mailbox-enable the admin account using Enable-Mailbox -Identity <admin ID>.
   • Check arbitration mailboxes with Get-Mailbox -Arbitration and recreate/fix any missing or unhealthy arbitration mailboxes as per the documented procedure.
4. HTTP 500 when creating mailboxes in EAC (role/permissions issue)
   If the error is specifically "500 Unexpected Error" when creating user mailboxes in EAC on Exchange Server 2016/2019, the fix is:
   • Update to Exchange Server 2016 CU21 or later, or Exchange Server 2019 CU10 or later.
   • If updating is not possible immediately, use one of these workarounds:
     • Add affected users to the View-Only Organization Management role group, or
     • Create a minimal custom role based on View-Only Configuration that only retains Get-RemoteDomain and assign it to Recipient Management users, or
     • Use Exchange Management Shell (New-Mailbox / Enable-Mailbox) instead of EAC.

Because the subscription and licenses are already active, further billing changes are not expected to resolve HTTP 500/X-OWA errors. The next steps should be taken by the Exchange/tenant administrator on the server side:

• Confirm which scenario above matches the symptoms (OWA usage, EAC sign-in, mailbox creation, or post-update failure).
• Apply the corresponding Exchange CU or security update fix.
• If relevant, verify admin and arbitration mailboxes as described.

If none of these documented cases match the exact environment, the issue likely requires tenant/server-level investigation by the Exchange or Microsoft 365 admin, including checking Exchange logs under %ExchangeInstallPath%\Logging\HttpProxy\Owa and engaging Microsoft Support.

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References:

• OWA error reporting responds with a HTTP error 500 in OwaSerializationException
• HTTP server error status (500) when signing in to EAC
• FIX: A client who uses Forefront Unified Access Gateway 2010 to browse to an Outlook Web App website may receive HTTP 500 errors intermittently instead of a Forefront Unified Access Gateway 2010 error page
• "500 Unexpected Error" when trying to create a user mailbox in Exchange admin center
• Fix failed Exchange Server updates