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  • 2004 The email address is no longer valid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 11 months ago

Message Delivery Failure Codes

Suggested Edits are limited on API Reference Pages

You can only suggest edits to Markdown body content, but not to the API spec.