Non-Delivery Reports
August 23 2007
Non-delivery reports are always submitted to the original sender of each email and also to an administrative person known as "postmaster@domain.com." The general structure of NDRs is defined in RFC 1893. Each NDR provides a 3-digit status notification code that defines the failure in detail. Each of these three digits provides information about the failure itself and can be translated as follows:
2.x.x: successful transfer
4.x.x: persistent failure
5.x.x: permanent failure
The following list describes second and third digit:
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 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 protocol 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 feature not supported
x.7.5: cryptographic failure
x.7.6: cryptographic algorithm not supported
x.7.7: message integrity failure