Internet Assigned Numbers Authority

Simple Mail Transfer Protocol (SMTP) Enhanced Status Codes Registry

Created
2008-05-29
Last Updated
2024-12-06
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Registries included below

Class Sub-Codes

Registration Procedure(s)
Specification Required
Expert(s)
Chris Newman
Reference
[RFC5248]
Available Formats

CSV
Code Summary Description Reference Submitter Change Controller
2.XXX.YYY Success Success specifies that the DSN is reporting a positive delivery action. Detail sub-codes may provide notification of transformations required for delivery. [RFC3463] (Standards track) G. Vaudreuil IESG
4.XXX.YYY Persistent Transient Failure A persistent transient failure is one in which the message as sent is valid, but persistence of some temporary condition has caused abandonment or delay of attempts to send the message. If this code accompanies a delivery failure report, sending in the future may be successful. [RFC3463] (Standards track) G. Vaudreuil IESG
5.XXX.YYY Permanent Failure A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery. [RFC3463] (Standards track) G. Vaudreuil IESG

Subject Sub-Codes

Registration Procedure(s)
Specification Required
Expert(s)
Chris Newman
Reference
[RFC5248]
Available Formats

CSV
Code Summary Description Reference Submitter Change Controller
X.0.YYY Other or Undefined Status There is no additional subject information available. [RFC3463] (Standards track) G. Vaudreuil IESG
X.1.YYY Addressing Status The address status reports on the originator or destination address. It may include address syntax or validity. These errors can generally be corrected by the sender and retried. [RFC3463] (Standards track) G. Vaudreuil IESG
X.2.YYY Mailbox Status Mailbox status indicates that something having to do with the mailbox has caused this DSN. Mailbox issues are assumed to be under the general control of the recipient. [RFC3463] (Standards track) G. Vaudreuil IESG
X.3.YYY Mail System Status Mail system status indicates that something having to do with the destination system has caused this DSN. System issues are assumed to be under the general control of the destination system administrator. [RFC3463] (Standards track) G. Vaudreuil IESG
X.4.YYY Network and Routing Status The networking or routing codes report status about the delivery system itself. These system components include any necessary infrastructure such as directory and routing services. Network issues are assumed to be under the control of the destination or intermediate system administrator. [RFC3463] (Standards track) G. Vaudreuil IESG
X.5.YYY Mail Delivery Protocol Status The mail delivery protocol status codes report failures involving the message delivery protocol. These failures include the full range of problems resulting from implementation errors or an unreliable connection. [RFC3463] (Standards track) G. Vaudreuil IESG
X.6.YYY Message Content or Media Status The message content or media status codes report failures involving the content of the message. These codes report failures due to translation, transcoding, or otherwise unsupported message media. Message content or media issues are under the control of both the sender and the receiver, both of which must support a common set of supported content-types. [RFC3463] (Standards track) G. Vaudreuil IESG
X.7.YYY Security or Policy Status The security or policy status codes report failures involving policies such as per-recipient or per-host filtering and cryptographic operations. Security and policy status issues are assumed to be under the control of either or both the sender and recipient. Both the sender and recipient must permit the exchange of messages and arrange the exchange of necessary keys and certificates for cryptographic operations. [RFC3463] (Standards track) G. Vaudreuil IESG

Enumerated Status Codes

Registration Procedure(s)
Specification Required
Expert(s)
Chris Newman
Reference
[RFC5248]
Available Formats

CSV
Code Sample Text Associated basic status code Description Reference Submitter Change Controller
X.0.0 Other undefined Status Any Other undefined status is the only undefined error code. It should be used for all errors for which only the class of the error is known. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.0 Other address status Not given Something about the address specified in the message caused this DSN. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.1 Bad destination mailbox address 451, 550 The mailbox specified in the address does not exist. For Internet mail names, this means the address portion to the left of the "@" sign is invalid. This code is only useful for permanent failures. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.2 Bad destination system address Not given The destination system specified in the address does not exist or is incapable of accepting mail. For Internet mail names, this means the address portion to the right of the "@" is invalid for mail. This code is only useful for permanent failures. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.3 Bad destination mailbox address syntax 501 The destination address was syntactically invalid. This can apply to any field in the address. This code is only useful for permanent failures. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.4 Destination mailbox address ambiguous Not given The mailbox address as specified matches one or more recipients on the destination system. This may result if a heuristic address mapping algorithm is used to map the specified address to a local mailbox name. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.5 Destination address valid 250 This mailbox address as specified was valid. This status code should be used for positive delivery reports. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.6 Destination mailbox has moved, No forwarding address Not given The mailbox address provided was at one time valid, but mail is no longer being accepted for that address. This code is only useful for permanent failures. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.7 Bad sender's mailbox address syntax Not given The sender's address was syntactically invalid. This can apply to any field in the address. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.8 Bad sender's system address 451, 501 The sender's system specified in the address does not exist or is incapable of accepting return mail. For domain names, this means the address portion to the right of the "@" is invalid for mail. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.1.9 Message relayed to non-compliant mailer Not given The mailbox address specified was valid, but the message has been relayed to a system that does not speak this protocol; no further information can be provided. [RFC3886] (Standards Track) E. Allman IESG
X.1.10 Recipient address has null MX 556 This status code is returned when the associated address is marked as invalid using a null MX. [RFC7505] (Standards Track); [RFC7504] (Standards Track) J. Levine, M. Delany, J. Klensin IESG
X.2.0 Other or undefined mailbox status Not given The mailbox exists, but something about the destination mailbox has caused the sending of this DSN. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.2.1 Mailbox disabled, not accepting messages Not given The mailbox exists, but is not accepting messages. This may be a permanent error if the mailbox will never be re-enabled or a transient error if the mailbox is only temporarily disabled. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.2.2 Mailbox full 552 The mailbox is full because the user has exceeded a per-mailbox administrative quota or physical capacity. The general semantics implies that the recipient can delete messages to make more space available. This code should be used as a persistent transient failure. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.2.3 Message length exceeds administrative limit 552 A per-mailbox administrative message length limit has been exceeded. This status code should be used when the per-mailbox message length limit is less than the general system limit. This code should be used as a permanent failure. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.2.4 Mailing list expansion problem 450, 452 The mailbox is a mailing list address and the mailing list was unable to be expanded. This code may represent a permanent failure or a persistent transient failure. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.3.0 Other or undefined mail system status 221, 250, 421, 451, 550, 554 The destination system exists and normally accepts mail, but something about the system has caused the generation of this DSN. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.3.1 Mail system full 452 Mail system storage has been exceeded. The general semantics imply that the individual recipient may not be able to delete material to make room for additional messages. This is useful only as a persistent transient error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.3.2 System not accepting network messages 453, 521 The host on which the mailbox is resident is not accepting messages. Examples of such conditions include an imminent shutdown, excessive load, or system maintenance. This is useful for both permanent and persistent transient errors. [RFC3463] (Standards Track); [RFC7504] (Standards Track) G. Vaudreuil, J. Klensin IESG
X.3.3 System not capable of selected features Not given Selected features specified for the message are not supported by the destination system. This can occur in gateways when features from one domain cannot be mapped onto the supported feature in another. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.3.4 Message too big for system 552, 554 The message is larger than per-message size limit. This limit may either be for physical or administrative reasons. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.3.5 System incorrectly configured Not given The system is not configured in a manner that will permit it to accept this message. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.3.6 Requested priority was changed 250 or 251 The message was accepted for relay/delivery, but the requested priority (possibly the implied default) was not honoured. The human readable text after the status code contains the new priority, followed by SP (space) and explanatory human readable text. [RFC6710] (Standards Track) A. Melnikov IESG
X.4.0 Other or undefined network or routing status Not given Something went wrong with the networking, but it is not clear what the problem is, or the problem cannot be well expressed with any of the other provided detail codes. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.4.1 No answer from host 451 The outbound connection attempt was not answered, because either the remote system was busy, or was unable to take a call. This is useful only as a persistent transient error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.4.2 Bad connection 421 The outbound connection was established, but was unable to complete the message transaction, either because of time-out, or inadequate connection quality. This is useful only as a persistent transient error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.4.3 Directory server failure 451, 550 The network system was unable to forward the message, because a directory server was unavailable. This is useful only as a persistent transient error. The inability to connect to an Internet DNS server is one example of the directory server failure error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.4.4 Unable to route Not given The mail system was unable to determine the next hop for the message because the necessary routing information was unavailable from the directory server. This is useful for both permanent and persistent transient errors. A DNS lookup returning only an SOA (Start of Administration) record for a domain name is one example of the unable to route error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.4.5 Mail system congestion 451 The mail system was unable to deliver the message because the mail system was congested. This is useful only as a persistent transient error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.4.6 Routing loop detected Not given A routing loop caused the message to be forwarded too many times, either because of incorrect routing tables or a user- forwarding loop. This is useful only as a persistent transient error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.4.7 Delivery time expired Not given The message was considered too old by the rejecting system, either because it remained on that host too long or because the time-to-live value specified by the sender of the message was exceeded. If possible, the code for the actual problem found when delivery was attempted should be returned rather than this code. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.5.0 Other or undefined protocol status 220, 250, 251, 252, 253, 451, 452, 454, 458, 459, 501, 502, 503, 554 Something was wrong with the protocol necessary to deliver the message to the next hop and the problem cannot be well expressed with any of the other provided detail codes. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.5.1 Invalid command 430, 500, 501, 503, 530, 550, 554, 555 A mail transaction protocol command was issued which was either out of sequence or unsupported. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.5.2 Syntax error 500, 501, 502, 550, 555 A mail transaction protocol command was issued which could not be interpreted, either because the syntax was wrong or the command is unrecognized. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.5.3 Too many recipients 451 More recipients were specified for the message than could have been delivered by the protocol. This error should normally result in the segmentation of the message into two, the remainder of the recipients to be delivered on a subsequent delivery attempt. It is included in this list in the event that such segmentation is not possible. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.5.4 Invalid command arguments 451, 501, 502, 503, 504, 550, 555 A valid mail transaction protocol command was issued with invalid arguments, either because the arguments were out of range or represented unrecognized features. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.5.5 Wrong protocol version Not given A protocol version mis-match existed which could not be automatically resolved by the communicating parties. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.5.6 Authentication Exchange line is too long 500 This enhanced status code SHOULD be returned when the server fails the AUTH command due to the client sending a [BASE64] response which is longer than the maximum buffer size available for the currently selected SASL mechanism. This is useful for both permanent and persistent transient errors. [RFC4954] (Standards Track) R. Siemborski, A. Melnikov IESG
X.6.0 Other or undefined media error Not given Something about the content of a message caused it to be considered undeliverable and the problem cannot be well expressed with any of the other provided detail codes. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.6.1 Media not supported Not given The media of the message is not supported by either the delivery protocol or the next system in the forwarding path. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.6.2 Conversion required and prohibited Not given The content of the message must be converted before it can be delivered and such conversion is not permitted. Such prohibitions may be the expression of the sender in the message itself or the policy of the sending host. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.6.3 Conversion required but not supported 554 The message content must be converted in order to be forwarded but such conversion is not possible or is not practical by a host in the forwarding path. This condition may result when an ESMTP gateway supports 8bit transport but is not able to downgrade the message to 7 bit as required for the next hop. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.6.4 Conversion with loss performed 250 This is a warning sent to the sender when message delivery was successfully but when the delivery required a conversion in which some data was lost. This may also be a permanent error if the sender has indicated that conversion with loss is prohibited for the message. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.6.5 Conversion Failed Not given A conversion was required but was unsuccessful. This may be useful as a permanent or persistent temporary notification. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.6.6 Message content not available 554 The message content could not be fetched from a remote system. This may be useful as a permanent or persistent temporary notification. [RFC4468] (Standards Track) C. Newman IESG
X.6.7 Non-ASCII addresses not permitted for that sender/recipient 553, 550 This indicates the reception of a MAIL or RCPT command that non-ASCII addresses are not permitted [RFC6531] (Standards track) Jiankang YAO ima@ietf.org
X.6.8 UTF-8 string reply is required, but not permitted by the SMTP client 252, 553, 550 This indicates that a reply containing a UTF-8 string is required to show the mailbox name, but that form of response is not permitted by the SMTP client. [RFC6531] (Standards track) Jiankang YAO ima@ietf.org
X.6.9 UTF-8 header message cannot be transferred to one or more recipients, so the message must be rejected 550 This indicates that transaction failed after the final "." of the DATA command. [RFC6531] (Standards track) Jiankang YAO ima@ietf.org
X.6.10 This is a duplicate of X.6.8 and is thus deprecated. [RFC6531] (Standards track)
X.7.0 Other or undefined security status 220, 235, 450, 454, 500, 501, 503, 504, 530, 535, 550 Something related to security caused the message to be returned, and the problem cannot be well expressed with any of the other provided detail codes. This status code may also be used when the condition cannot be further described because of security policies in force. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.1 Delivery not authorized, message refused 451, 454, 502, 503, 533, 550, 551 The sender is not authorized to send to the destination. This can be the result of per-host or per-recipient filtering. This memo does not discuss the merits of any such filtering, but provides a mechanism to report such. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.2 Mailing list expansion prohibited 550 The sender is not authorized to send a message to the intended mailing list. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.3 Security conversion required but not possible Not given A conversion from one secure messaging protocol to another was required for delivery and such conversion was not possible. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.4 Security features not supported 504 A message contained security features such as secure authentication that could not be supported on the delivery protocol. This is useful only as a permanent error. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.5 Cryptographic failure Not given A transport system otherwise authorized to validate or decrypt a message in transport was unable to do so because necessary information such as key was not available or such information was invalid. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.6 Cryptographic algorithm not supported Not given A transport system otherwise authorized to validate or decrypt a message was unable to do so because the necessary algorithm was not supported. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.7 Message integrity failure Not given A transport system otherwise authorized to validate a message was unable to do so because the message was corrupted or altered. This may be useful as a permanent, transient persistent, or successful delivery code. [RFC3463] (Standards Track) G. Vaudreuil IESG
X.7.8 Authentication credentials invalid 535, 554 This response to the AUTH command indicates that the authentication failed due to invalid or insufficient authentication credentials. In this case, the client SHOULD ask the user to supply new credentials (such as by presenting a password dialog box). [RFC4954] (Standards Track) R. Siemborski, A. Melnikov IESG
X.7.9 Authentication mechanism is too weak 534 This response to the AUTH command indicates that the selected authentication mechanism is weaker than server policy permits for that user. The client SHOULD retry with a new authentication mechanism. [RFC4954] (Standards Track) R. Siemborski, A. Melnikov IESG
X.7.10 Encryption Needed 523 This indicates that external strong privacy layer is needed in order to use the requested authentication mechanism. This is primarily intended for use with clear text authentication mechanisms. A client which receives this may activate a security layer such as TLS prior to authenticating, or attempt to use a stronger mechanism. [RFC5248] (Best current practice) T. Hansen, J. Klensin IESG
X.7.11 Encryption required for requested authentication mechanism 524, 538 This response to the AUTH command indicates that the selected authentication mechanism may only be used when the underlying SMTP connection is encrypted. Note that this response code is documented here for historical purposes only. Modern implementations SHOULD NOT advertise mechanisms that are not permitted due to lack of encryption, unless an encryption layer of sufficient strength is currently being employed. [RFC4954] (Standards Track) R. Siemborski, A. Melnikov IESG
X.7.12 A password transition is needed 422, 432 This response to the AUTH command indicates that the user needs to transition to the selected authentication mechanism. This is typically done by authenticating once using the [PLAIN] authentication mechanism. The selected mechanism SHOULD then work for authentications in subsequent sessions. [RFC4954] (Standards Track) R. Siemborski, A. Melnikov IESG
X.7.13 User Account Disabled 525 Sometimes a system administrator will have to disable a user's account (e.g., due to lack of payment, abuse, evidence of a break-in attempt, etc). This error code occurs after a successful authentication to a disabled account. This informs the client that the failure is permanent until the user contacts their system administrator to get the account re-enabled. It differs from a generic authentication failure where the client's best option is to present the passphrase entry dialog in case the user simply mistyped their passphrase. [RFC5248] (Best current practice) T. Hansen, J. Klensin IESG
X.7.14 Trust relationship required 535, 554 The submission server requires a configured trust relationship with a third-party server in order to access the message content. This value replaces the prior use of X.7.8 for this error condition. thereby updating [RFC4468]. [RFC5248] (Best current practice) T. Hansen, J. Klensin IESG
X.7.15 Priority Level is too low 450, 550 (other 4XX or 5XX codes are allowed) The specified priority level is below the lowest priority acceptable for the receiving SMTP server. This condition might be temporary, for example the server is operating in a mode where only higher priority messages are accepted for transfer and delivery, while lower priority messages are rejected. [RFC6710] (Standards Track) A. Melnikov IESG
X.7.16 Message is too big for the specified priority 552 (other 4XX or 5XX codes are allowed) The message is too big for the specified priority. This condition might be temporary, for example the server is operating in a mode where only higher priority messages below certain size are accepted for transfer and delivery. [RFC6710] (Standards Track) A. Melnikov IESG
X.7.17 Mailbox owner has changed 5XX This status code is returned when a message is received with a Require-Recipient-Valid-Since field or RRVS extension and the receiving system is able to determine that the intended recipient mailbox has not been under continuous ownership since the specified date-time. [RFC7293] (Standards Track) M. Kucherawy IESG
X.7.18 Domain owner has changed 5XX This status code is returned when a message is received with a Require-Recipient-Valid-Since field or RRVS extension and the receiving system wishes to disclose that the owner of the domain name of the recipient has changed since the specified date-time. [RFC7293] (Standards Track) M. Kucherawy IESG
X.7.19 RRVS test cannot be completed 5XX This status code is returned when a message is received with a Require-Recipient-Valid-Since field or RRVS extension and the receiving system cannot complete the requested evaluation because the required timestamp was not recorded. The message originator needs to decide whether to reissue the message without RRVS protection. [RFC7293] (Standards Track) M. Kucherawy IESG
X.7.20 No passing DKIM signature found 550 This status code is returned when a message did not contain any passing DKIM signatures. (This violates the advice of Section 6.1 of [RFC6376].) [RFC7372] (Standards Track); [RFC6376] (Standards Track) M. Kucherawy IESG
X.7.21 No acceptable DKIM signature found 550 This status code is returned when a message contains one or more passing DKIM signatures, but none are acceptable. (This violates the advice of Section 6.1 of [RFC6376].) [RFC7372] (Standards Track); [RFC6376] (Standards Track) M. Kucherawy IESG
X.7.22 No valid author-matched DKIM signature found 550 This status code is returned when a message contains one or more passing DKIM signatures, but none are acceptable because none have an identifier(s) that matches the author address(es) found in the From header field. This is a special case of X.7.21. (This violates the advice of Section 6.1 of [RFC6376].) [RFC7372] (Standards Track); [RFC6376] (Standards Track) M. Kucherawy IESG
X.7.23 SPF validation failed 550 This status code is returned when a message completed an SPF check that produced a "fail" result, contrary to local policy requirements. Used in place of 5.7.1 as described in Section 8.4 of [RFC7208]. [RFC7372] (Standards Track); [RFC7208] (Standards Track) M. Kucherawy IESG
X.7.24 SPF validation error 451/550 This status code is returned when evaluation of SPF relative to an arriving message resulted in an error. Used in place of 4.4.3 or 5.5.2 as described in Sections 8.6 and 8.7 of [RFC7208]. [RFC7372] (Standards Track); [RFC7208] (Standards Track) M. Kucherawy IESG
X.7.25 Reverse DNS validation failed 550 This status code is returned when an SMTP client's IP address failed a reverse DNS validation check, contrary to local policy requirements. [RFC7372], Section 3.3 (Standards Track) M. Kucherawy IESG
X.7.26 Multiple authentication checks failed 550 This status code is returned when a message failed more than one message authentication check, contrary to local policy requirements. The particular mechanisms that failed are not specified. [RFC7372] (Standards Track) M. Kucherawy IESG
X.7.27 Sender address has null MX 550 This status code is returned when the associated sender address has a null MX, and the SMTP receiver is configured to reject mail from such sender (e.g., because it could not return a DSN). [RFC7505] (Standards Track) J. Levine, M. Delany IESG
X.7.28 Mail flood detected . The message appears to be part of a mail flood of similar abusive messages. [draft-levine-mailbomb-header-00] J. Levine standards@taugh.com
X.7.29 ARC validation failure 550 This status code may be returned when a message fails ARC validation. [RFC8617] K. Andersen IESG
X.7.30 REQUIRETLS support required 550 This indicates that the message was not able to be forwarded because it was received with a REQUIRETLS requirement and none of the SMTP servers to which the message should be forwarded provide this support. [RFC8689] J. Fenton IESG