DSNs are standardized messages that report delivery success, delay, or failure. Learn how DSNs work and what common DSN codes mean.
A Delivery Status Notification (DSN) is a standardized message that reports the outcome of an email delivery attempt. DSNs can indicate successful delivery, delays, or permanent failures (bounces).
DSNs usually include SMTP status codes and diagnostic text that helps pinpoint the cause, such as invalid mailbox, blocked sender, or policy rejection. This information is essential for troubleshooting deliverability and cleaning lists.
Not every system sends DSNs the same way, but the codes are often consistent enough to categorize issues as hard or soft failures. Using DSN insights to suppress hard bounces quickly is a core best practice.