A non-delivery report is an automated diagnostic message sent back to the original sender when an email fails to reach its destination. It contains specific error codes and text explaining the failure, such as an invalid address, a full mailbox, or a blocked domain. Administrators rely on the headers and status codes inside these reports to troubleshoot mail routing issues.
Heard on the job
Check the NDR to see if the remote server rejected the attachment for being too large.
Insider tip
Users often ignore the text in an NDR and just complain that email is broken. Always ask them to forward the exact bounce message, as the SMTP error code inside tells you exactly what went wrong.
Also heard as
- non-delivery receipt
- bounce message