Emails sent using Outlook Desktop results in Non-Delivery Report [0x80040305-0x00000000-0x00000000]

Last Updated: December 7, 2023

ISSUE

When using Outlook Desktop to send an email, you get an unexpected Non-Delivery Report (NDR) that includes the error code 0x80040305. For example: 
 
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Your message did not reach some or all of the intended recipients. 

      Subject:      Email subject

      Sent:             12/7/2023 3:17 PM 

The following recipient(s) cannot be reached: 

       recipient@contoso.com on 12/7/2023 3:17 PM 

This message could not be sent. Try sending the message again later or contact your network administrator. 

 __________________________________________________ 

 Diagnostic information for administrators: 
__________________________________________________ 

 Error is [0x80040305-0x00000000-0x00000000]. 

Submit-Message failed: message id(1), failure enum(1), HResult(0x80040305), EC(1246). 

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This issue is like the prior 500 folder limit that the Outlook Team fixed, Lifting the 500 Folder Limit in Outlook. That solution targeted shared folders but did not include the scenario occurring in the user’s primary mailbox.

STATUS: INVESTIGATING

The Outlook Team is investigating the issue. We will update this topic as soon as we have any status updates.

WORKAROUND

To workaround the issue, you can apply the appropriate recommendations: 

• Reduce the number of folders which have subfolders to under 500. We recommend no more than 450 nested folders while we continue to investigate.

• Keep folders collapsed instead of expanded.

  • If you can’t do either of the above, avoid subsequent online actions in Outlook. Such actions include using the buttons for “View on Server” and “Click here to view more on Microsoft Exchange”, or use of “Include older results” when searching.

  • If you use any of these actions, restart Outlook immediately for best performance.