Message Delivery Failure Codes

When messages bounce or fail in either the On-Demand service or in an On-Premise system, failure codes are provided in order to indicate the nature of the bounce or failure. On-Premise systems also allow these codes to be customized, as described in our article Modifying, Adding or Customizing Failure Codes.

Message Rejected

The message was rejected by recipient’s mail server.

  • 1002-1003 Your message was rejected because it was associated with a blacklist
  • 1004 Your message was rejected due to its content
  • 1006 Too many connections in a period of time
  • 1007 A virus was detected in your message
  • 1011 Challenge responses requests
  • 1999 Your message was rejected for a reason not specified above

Permanent Failures

A recipient’s address was found to be invalid.

  • 2001 The email address is invalid
  • 2002 The domain of the email address is invalid
  • 2003 The email address is not in a valid format
  • 2004 The email address is no longer valid
  • 2999 The email address was rejected for a reason not specified above

Temporary Failures

Delivery to the recipient’s address is temporarily unavailable.

  • 3001 The recipient's mailbox is full or over quota
  • 3002 Recipient email account is inactive/disabled
  • 3003 Recipient’s server continuously asked us to “try later”
  • 3999 The email address was rejected for a reason not specified above

Communication Failures

System, network or protocol errors preventing delivery.

  • 4001 Recipient’s server too busy
  • 4002 Protocol error, invalid command or timeout
  • 4003 Unable to connect to recipient's mail server
  • 4004 Recipient’s server rejected message as too old
  • 4006 Your message was rejected because the receiving server is not accepting mail for the destination domain
  • 4999 A system, network or protocol error prevented the delivery of your message for a reason not specified above


Not errors, necessarily, but automated responses designed to provide information

  • 5001 Out of office / Auto-reply
  • 5999 An informational message was received other than for a reason specified above


Indicates that no other failure codes were encountered.

  • 9999 The reason for the failure is unknown.

Updated about a year ago

Message Delivery Failure Codes

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