Analyze non-delivery reports (NDRs)

Non-delivery reports, also known as bounce messages, are automatically generated when a message fails to reach its intended recipient. NDRs provide valuable information about why a message failed, enabling administrators to identify and resolve underlying issues. These reports are usually sent to the sender, informing them of the delivery failure.

Common NDR Scenarios:

1. Invalid Recipient Address:

   One of the most common reasons for NDRs is an invalid recipient email address. The NDR will typically indicate that the email address does not exist or that the domain is not found.

   Example NDR:
550 5.1.1 : Recipient address rejected: User unknown in local recipient table


2. Message Size Exceeded:

   NDRs may occur if the email message exceeds the maximum allowed size. The report will indicate that the message was rejected due to size limitations.

   Example NDR:
552 5.3.4 : Message size exceeds maximum permitted


3. Temporary Delivery Failure:

   In some cases, email delivery failures are temporary. NDRs will notify the sender that the message could not be delivered at that particular time.

   Example NDR:
450 4.7.1 : Temporary failure. Please try again later.


Analyzing NDRs:

When troubleshooting email delivery problems, analyzing NDRs can provide valuable insights. Here are some key steps to analyze NDRs effectively:

1. Understand the NDR Code:

   NDRs include error codes that provide specific information about the failure. These codes help administrators identify the cause and decide the appropriate action for resolution. Microsoft provides a comprehensive list of NDR codes in their documentation.

2. Examine the Reason for Failure:

   NDRs often include a brief explanation of why the message failed. This information can assist administrators in diagnosing the root cause of the issue. Analyzing the reason for failure can help identify issues such as mailbox size limits, recipient’s address typos, or problems with the sender’s IP reputation.

3. Check the Diagnostic Information:

   NDRs may contain additional diagnostic information, such as server names, timestamps, or firewall-related details. This information can be valuable when investigating delivery failures further. Administrators can use this data to trace the message path and identify potential bottlenecks.

4. Review the Delivery Timeline:

   NDRs include timestamps indicating when each delivery attempt was made. By analyzing the delivery timeline, administrators can determine if the issue is temporary or if further action is required. They can also identify patterns, such as repeated delivery attempts or delays at specific stages of the message delivery process.

Resolving NDR Issues:

Once the cause of a delivery failure is identified through NDR analysis, administrators can take the following steps to resolve the issue:

1. Check Recipient and Sender Email Addresses:

   Ensure the recipient’s email address is correct and that there are no typos. Also, verify that the sender’s address is valid and properly configured.

2. Address Size Limitations:

   If the NDR indicates a message size limit exceeded, consider reducing the message size by removing attachments or compressing files. Alternatively, you can share large files via cloud storage and send a link instead.

3. Retry Delivery:

   If the NDR indicates a temporary delivery failure, you can attempt to resend the message after some time. The temporary failure could be due to server congestion, network issues, or the recipient’s mailbox being temporarily unavailable.

4. Contact Technical Support:

   For persistent or complex delivery failures, reaching out to Microsoft’s technical support can provide expert assistance. They can help troubleshoot the issue, analyze logs, and provide guidance for a resolution.

Conclusion:

Analyzing NDRs is a critical step in troubleshooting email delivery issues within Microsoft 365 Messaging. By understanding the codes, examining the reasons for failure, and reviewing diagnostic information, administrators gain valuable insights into the underlying problems. With this information, they can take appropriate action to resolve the issues and ensure smooth email communication within their organization.