I am having Error 500 come up when I attempt to open my Outlook

Hi @Reception TC Dental, 

I hope you're having a productive day.  

Thank you for reaching out regarding the error message you’re encountering when signing in to Outlook.  

Regarding the "Error 500" you are experiencing, this typically indicates a server-side or account-related issue rather than a problem with your browser or device. More specifically, this error commonly occurs when an account does not have an assigned Exchange Online mailbox or when the required Microsoft 365 license, which includes Exchange Online services, is missing or inactive. Without a valid mailbox and the appropriate license in place, Outlook on the web is unable to load your email data, which ultimately results in this error appearing. Since you have already taken the initiative to uninstall, redownload, and restart your device, the next logical step is to review your account and service configuration. 

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: 

• 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.  

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. 

Afterward, it's recommended that the administrator verify the mailbox exists using:  

Get-Mailbox -Identity ******@domain.com  

If no mailbox exists, create one:  

New-Mailbox -UserPrincipalName ******@domain.com -FirstName 'First' -LastName 'Last'  

Please try opening Outlook through Outlook Web Access (OWA) in incognito mode to see if you can access it once the mailbox and license are correctly configured. 

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.  

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. Wishing you a smooth rest of your day. 

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have any extra questions about this answer, please click "Comment".             

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Follow these steps in order, testing Outlook after each step:

1. Run the Outlook startup troubleshooter (classic Outlook)
   Since Outlook for Windows (classic) works for many users when new Outlook has issues, first confirm classic Outlook can start:
   • Use the classic Outlook startup troubleshooter for Windows to automatically diagnose and fix common startup issues: select Start in the article and follow the prompts in Get Help.
   • Details and requirements are in: “I can’t start Microsoft Outlook or receive the error ‘Cannot start Microsoft Outlook. Cannot open the Outlook Window’.”
2. Start Outlook in Safe Mode and disable add-ins (classic Outlook)
   If classic Outlook is also affected or you get a similar startup problem:
   • Press Windows key + R.
   • Type Outlook /safe and select OK.
   • Accept the default profile and sign in if prompted.
   • If Outlook opens in safe mode, disable add-ins:
     1. Go to File > Options > Add-ins.
     2. At the bottom, ensure Manage: COM Add-ins is selected and choose Go.
     3. Record which add-ins are checked (or take a screenshot).
     4. Clear all check boxes and select OK.
     5. Close Outlook and start it normally.
   • If Outlook now opens, re-enable add-ins one at a time, restarting Outlook each time, until the problem reappears. The last add-in enabled is the cause; leave it disabled.
3. Create a new Outlook profile
   If Outlook still fails to start or shows error 500 on startup, the profile may be corrupted:
   • Follow the steps in Create an Outlook profile (linked from the “I get a ‘stopped working’ error when I start Office applications on my PC” article) to create a new profile and re-add accounts.
4. Delete local Outlook/OneAuth cache for new Outlook
   For the new Outlook for Windows specifically, if the error 500 appears before sign-in even after reinstalling, clear the local cache used by new Outlook:
   • Close all Microsoft apps (Outlook, Teams, etc.).
   • Press Windows + R, type appdata, and press Enter.
   • Go to Local > Microsoft > Olk and delete the Olk folder.
   • Go to Local > Microsoft > OneAuth and delete the OneAuth folder.
   • Restart the computer.
   • Open Outlook again and sign in. These folders are recreated automatically and often resolve persistent startup issues in new Outlook after reinstall/repair.
5. Repair or reinstall Office if needed
   If the error persists across both classic and new Outlook:
   • Run a Quick Repair of Office first; if that fails, run an Online Repair as described in Repair an Office application.
   • If repair does not help, fully uninstall Office and reinstall, as described in I get a “stopped working” error when I start Office applications on my PC. If the standard uninstall does not fully remove Office, use the Microsoft 365 uninstall troubleshooter or the manual uninstall steps referenced there.
6. If the issue is tenant-side (HTTP 500 from service)
   If the 500 error is a server-side “TenantAccessBlockedError” or similar (seen in some Outlook/Teams sign-in scenarios), it can be temporary or tenant-policy related. In a business environment, wait a short period and try again; if it persists, contact the Microsoft 365 admin to check tenant health and access status.

If, after these steps, new Outlook still shows error 500 at startup while classic Outlook works, continue using classic Outlook temporarily and escalate through Microsoft 365 support with the full error details.

References:

• I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window”
• Start Outlook in safe mode and disable add-ins
• I get a "stopped working" error when I start Office applications on my PC
• Outlook send/receive errors HTTP 0, HTTP 404, HTTP 500
• Detected a problem launching new Outlook - Microsoft Q&A
• Tried loggin into Teams and Outlook and got this message on outlook, and unable to log into teams. - Microsoft Q&A
• How can I get office 365 to work? - Microsoft Q&A