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How does Postfix format DSNs?

  • Postfix DSN format follows RFC standards with specific characteristics:
  • Structure:
  • MIME multipart/report format. Three parts: human-readable, machine-readable, original message.
  • Human-readable part:
  • Plain text explanation. Server name and timestamp. Error description.
  • Machine-readable part (message/delivery-status):
  • Per-recipient fields. Status codes. Diagnostic code. Remote MTA information.
  • Original message part:
  • Headers of failed message. Sometimes full message body.
  • Typical Postfix bounce header:
  • From: MAILER-DAEMON@domain.com. Subject: Undelivered Mail Returned to Sender. Includes queue ID and timestamps.
  • Parsing tips:
  • Look for "Status:" field for code. "Diagnostic-Code:" for details. "Final-Recipient:" for address.
  • Postfix follows RFC 3464 closely. Standard parsing works well with Postfix DSNs.
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