Bounce Handling

• Backscatter and BATV

  Misdirected bounces to forged return-paths — why accept-then-bounce causes it, how Backscatterer.org listings work, BATV prvs= tagging mechanics (draft-levine-smtp-batv-01) with operational pros/cons, and modern alternatives.

• Delivery Status Notifications — DSN Format (RFC 3464)

  How bounce messages are structured: the multipart/report DSN format, per-message and per-recipient fields (Action, Status, Diagnostic-Code), and how senders should parse them.

• SMTP Enhanced Status Codes (RFC 3463)

  The X.Y.Z enhanced mail system status code taxonomy — classes, subjects, and the full detail-code table — and how to use it for bounce classification.