Non-Delivery Report


A Non-Delivery Report (NDR) is a notification generated by an email system to inform the sender that their message failed to be delivered to the intended recipient. This can occur due to various reasons such as incorrect email addresses, mailbox quota issues, or server problems. The NDR typically contains error codes and a description that helps identify the cause of the delivery failure.

Key Takeaways

  1. A Non-Delivery Report (NDR) is an automatic notification generated by email servers to notify the sender that their message could not be delivered to the intended recipient.
  2. NDRs are often triggered by various reasons such as incorrect email address, recipient’s mailbox being unavailable or full, server failures, or email content being flagged as suspicious.
  3. It is essential to follow the best email practices, double-check the recipient addresses, and ensure proper email server configuration to minimize the chances of receiving Non-Delivery Reports.


The technology term Non-Delivery Report (NDR) is important as it serves as an automated notification sent by a mail system to inform the sender that their email failed to be delivered.

NDRs play an essential role in preserving effective email communication by alerting users of issues such as incorrect email addresses, network problems, or spam filters blocking the email.

By emphasizing these errors, NDRs enable the sender to take necessary corrective actions, such as updating contact information or resolving technical issues, thus enhancing the overall effectiveness and reliability of email correspondence.


A Non-Delivery Report (NDR) is crucial for maintaining the efficiency, reliability, and integrity of electronic communications, particularly in the realm of email exchange. The purpose of an NDR is to notify the sender that their message has not been successfully delivered to the intended recipient, thus indicating the existence of an issue or obstacle in the delivery process.

Common reasons for an NDR include an incorrect or non-existent email address, a recipient’s mailbox being full, or a problem with the mail server, among others. By sending an NDR, the sender is informed that their message has not reached its destination, enabling them to take necessary corrective actions, such as reconfirming the recipient’s email address or attempting another method of communication.

Beyond simply acting as a notification, NDRs also provide diagnostic information and details about the cause of the delivery failure. This information can shed light on the underlying issues or obstacles in the message transmission process, hence guiding the sender or the system administrator in effectively resolving those issues.

Furthermore, the use of NDRs contributes to the optimal utilization of network resources by preventing the clutter of undeliverable messages, ensuring that bandwidth is allocated to genuine communication and relevant data exchange. Consequently, Non-Delivery Reports play an indispensable role in maintaining the overall functionality and accessibility of email and other electronic communication systems.

Examples of Non-Delivery Report

A Non-Delivery Report (NDR), also known as a Non-Delivery Receipt, is a notification generated by an email server when it fails to deliver an email message to the intended recipient. Here are three real-world examples of situations that might result in a Non-Delivery Report:

Incorrect Email Address: Alice sends an email to her colleague Bob, but she accidentally mistypes Bob’s email address. Instead of [email protected], she types [email protected]. The email server detects that the address does not exist and bounces the email back to Alice, along with an NDR informing her that her message has not been delivered.

Recipient’s Mailbox is Full: Alice sends an email to her client Carol, who has not cleared her inbox in a while. Carol’s mailbox is now full, and she cannot receive any new emails. When Alice’s message arrives at Carol’s email server, the server generates an NDR informing Alice that her message could not be delivered because the recipient’s mailbox is full.

Blocked by Spam Filter: Alice sends an email to her vendor Dave but unknowingly includes a word, phrase, or attachment that triggers Dave’s email server’s spam filter. As a result, Dave’s server blocks the email and sends an NDR to Alice, indicating that her message has been considered spam and thus not delivered.

Non-Delivery Report FAQ

1. What is a Non-Delivery Report?

A Non-Delivery Report (NDR) is an automated email message sent by an email server to the sender when an email could not be delivered to the intended recipient. NDRs provide information about the reasons for the failure and helps the sender diagnose and fix the problem.

2. What are the common reasons for receiving a Non-Delivery Report?

Some common reasons for receiving a Non-Delivery Report include an incorrect email address, a full recipient mailbox, email server connectivity issues, or content filtering. These factors can prevent the email from being delivered successfully.

3. How can I fix a Non-Delivery Report issue?

To fix a Non-Delivery Report issue, first identify the reason for the NDR by reviewing the error message/code. Then, you may need to correct the email address, contact the recipient to clear their mailbox, investigate server issues, or check the content of your email for potential filtering triggers.

4. Will my email be automatically resent after receiving a Non-Delivery Report?

No, your email will not be automatically resent after receiving an NDR. You must identify and resolve the issue, then resend the email yourself. This helps prevent sending multiple unnecessary emails to the recipient.

5. Can I prevent Non-Delivery Reports?

While it may not be possible to prevent all NDRs, you can minimize their likelihood by maintaining up-to-date contact information, regularly checking your outgoing messages for accuracy, and adhering to best practices for email content and formatting.

Related Technology Terms

  • Email Bounce
  • Mail Delivery Failure
  • Undeliverable Email
  • Bounced Message Notification
  • SMTP Error Report

Sources for More Information

  • Microsoft: Microsoft provides extensive documentation on non-delivery reports, especially in the context of their email services such as Exchange and Office 365.
  • SendGrid: SendGrid is an email platform that offers valuable insights and guides on handling non-delivery reports and improving email delivery.
  • IETF RFCs: The Internet Engineering Task Force (IETF) provides Request for Comments (RFC) documents that contain technical and organizational notes, including standardization of non-delivery reports.
  • Postfix: Postfix, a popular open-source email server, has documentation and discussions on non-delivery reports, which can provide detailed information on the topic.

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