DSN codes classify delivery failures like 5.1.1 user unknown. Learn what DSN codes mean and how to use them.
DSN bounce codes are standardized status codes that explain delivery outcomes. They often appear as enhanced status codes like 5.1.1 (bad mailbox) or 4.2.2 (mailbox full).
These codes help automate bounce classification and suppression rules. Using DSN codes improves accuracy compared to parsing free-form bounce text alone.