Understanding DSNs and NDRs

Common Enhanced Status Codes

  • 4.3.1 – Insufficient system resources
  • 4.3.2 – System not accepting network messages
  • 4.4.1 – Connection timed out
  • 4.4.2 – Connection dropped
  • 4.4.7 – Message expired
  • 5.0.0 – HELO / EHLO requires domain address
  • 5.1.0 – Sender denied
  • 5.1.1 – Bad destination mailbox address
  • 5.1.2 – Invalid X.400 address
  • 5.1.3 – Invalid recipient address
  • 5.1.4 – Destination mailbox address ambiguous
  • 5.1.7 – Invalid address
  • 5.2.1 – Mailbox cannot be accessed
  • 5.2.2 – Mailbox full
  • 5.2.3 – Message too large
  • 5.2.4 – Mailing list expansion problem
  • 5.3.3 – Unrecognized command
  • 5.3.4 – Message too big for system
  • 5.3.5 – System incorrectly configured
  • 5.4.4 – Invalid arguments
  • 5.4.6 – Routing loop detected
  • 5.5.2 – Send hello first
  • 5.5.3 – Too many recipients
  • 5.5.4 – Invalid domain name
  • 5.5.6 – Invalid message content
  • 5.7.1 – Delivery not authorized
  • 5.7.1 – Unable to relay
  • 5.7.1 – Client was not authenticated
  • 5.7.3 – Not Authorized

More about understanding DSNs and NDRs

Enhanced Status Codes for Delivery
Request for Comments (RFC) 1893 provides an enhanced set of status codes for Delivery Status Notification (DSN) messages. This is an extension of the coding defined in RFC 821. The error codes in RFC 821 are designed to deal with messaging, and are not as useful for DSN messages. The code specified in the “More Information” section provides a more specific, flexible system of coding for DSN messages (non-delivery reports, read and delivery receipts, and so on). The Enhanced Status Codes provide a standard mechanism for reporting mail system errors, and provide more meaningful information than the standard error codes defined in the SMTP RFC (821).

2.X.X Success
4.X.X Persistent Transient Failure
5.X.X Permanent Failure

X.1.0 Other address status
X.1.1 Bad destination mailbox address
X.1.2 Bad destination system address
X.1.3 Bad destination mailbox address syntax
X.1.4 Destination mailbox address ambiguous
X.1.5 Destination mailbox address valid
X.1.6 Mailbox has moved
X.1.7 Bad sender’s mailbox address syntax
X.1.8 Bad sender’s system address

X.2.0 Other or undefined mailbox status
X.2.1 Mailbox disabled, not accepting messages
X.2.2 Mailbox full
X.2.3 Message length exceeds administrative limit
X.2.4 Mailing list expansion problem

X.3.0 Other or undefined mail system status
X.3.1 Mail system full
X.3.2 System not accepting network messages
X.3.3 System not capable of selected features
X.3.4 Message too big for system

X.4.0 Other or undefined network or routing status
X.4.1 No answer from host
X.4.2 Bad connection
X.4.3 Routing server failure
X.4.4 Unable to route
X.4.5 Network congestion
X.4.6 Routing loop detected
X.4.7 Delivery time expired

X.5.0 Other or undefined protocol status
X.5.1 Invalid command
X.5.2 Syntax error
X.5.3 Too many recipients
X.5.4 Invalid command arguments
X.5.5 Wrong protocol version

X.6.0 Other or undefined media error
X.6.1 Media not supported
X.6.2 Conversion required and prohibited
X.6.3 Conversion required but not supported
X.6.4 Conversion with loss performed
X.6.5 Conversion failed

X.7.0 Other or undefined security status
X.7.1 Delivery not authorized, message refused
X.7.2 Mailing list expansion prohibited
X.7.3 Security conversion required but not possible
X.7.4 Security features not supported
X.7.5 Cryptographic failure
X.7.6 Cryptographic algorithm not supported
X.7.7 Message integrity failure

More about enhanced Status Codes for Delivery – RFC 1893