Datasets:

blazalek
/

open-smtp-error-dataset

record_id string	enhanced_status_code string	registry_pattern string	catalog_url string	category_id string	outcome_class string	retry_decision string	suppression_decision string	title string	short_description string	tldr string	content_json string	related_codes_json string	classification_rule_key string	classification_failure_persistence string	classification_cause_family string	classification_recipient_validity string	classification_retry_disposition string	classification_suppression_disposition string	classification_confidence string	classification_needs_review string
email-error-2-0-0	2.0.0	X.0.0	https://blazalek.com/en/email-errors/2-0-0	other-undefined	success	do_not_retry	check_context	Other undefined success status	Code 2.0.0 is a general success status: only class 2 is known, with no more specific status. It is not a message rejection.	Generic success status when only class 2 is known. Treat it as acceptance, not rejection: misclassifying it as a bounce breaks deliverability reporting. This is not a failure; do not retry, and list hygiene is unaffected unless your system wrongly routes it to bounce handling.	{"title":"Other undefined success status","short_description":"Code 2.0.0 is a general success status: only class 2 is known, with no more specific status. It is not a message rejection.","tldr":"Generic success status when only class 2 is known. Treat it as acceptance, not rejection: misclassifying it as a bounce brea...	["4.0.0","5.0.0"]	esc-2-0-0	indeterminate	unknown	unverified	do_not_retry	no_recommendation	low	true
email-error-2-1-5	2.1.5	X.1.5	https://blazalek.com/en/email-errors/2-1-5	addressing	success	do_not_retry	check_context	2.1.5 — Destination address is valid	The specified recipient mailbox address was found to be valid. This is a success confirmation, not a message rejection.	Confirms the recipient mailbox address is valid in a positive delivery report. Important for correlating message events; this is success, not rejection. Do not retry or suppress on this code alone: deliverability and list hygiene are unaffected.	{"title":"2.1.5 — Destination address is valid","short_description":"The specified recipient mailbox address was found to be valid. This is a success confirmation, not a message rejection.","tldr":"Confirms the recipient mailbox address is valid in a positive delivery report. Important for correlating message events; t...	["4.1.1","4.1.8","5.1.1","5.1.3"]	esc-2-1-5	indeterminate	unknown	valid	do_not_retry	no_recommendation	high	false
email-error-2-3-0	2.3.0	X.3.0	https://blazalek.com/en/email-errors/2-3-0	mail-system	success	do_not_retry	check_context	2.3.0 — Other or undefined mail system status	The destination system exists and normally accepts mail, but its condition caused a general DSN to be generated. Because the code begins with 2, it describes success, not a message rejection.	General mail-system status in success class 2: not a delivery failure. Operationally informational; if your tools label it a bounce, fix event mapping. Accepted result: do not retry. Deliverability and reputation are usually unaffected.	{"title":"2.3.0 — Other or undefined mail system status","short_description":"The destination system exists and normally accepts mail, but its condition caused a general DSN to be generated. Because the code begins with 2, it describes success, not a message rejection.","tldr":"General mail-system status in success cla...	["4.3.0","5.3.0","2.3.6","4.3.1"]	esc-2-3-0	indeterminate	unknown	unverified	do_not_retry	no_recommendation	low	true
email-error-2-3-6	2.3.6	X.3.6	https://blazalek.com/en/email-errors/2-3-6	mail-system	success	do_not_retry	check_context	2.3.6 — Requested priority was changed	The message was accepted for relay or delivery, but the requested priority—including a possible implied default—was not retained. The system reported a new priority instead. This is a success status, not a rejection.	The message was accepted, but the requested priority was changed: success, not rejection. Note the new priority operationally. Do not retry. Deliverability and list hygiene are unaffected; this status is informational.	{"title":"2.3.6 — Requested priority was changed","short_description":"The message was accepted for relay or delivery, but the requested priority—including a possible implied default—was not retained. The system reported a new priority instead. This is a success status, not a rejection.","tldr":"The message was accepte...	["2.3.0","4.3.0","4.3.1","4.3.2"]	esc-2-3-6	indeterminate	unknown	unverified	do_not_retry	no_recommendation	high	true
email-error-2-5-0	2.5.0	X.5.0	https://blazalek.com/en/email-errors/2-5-0	delivery-protocol	success	do_not_retry	check_context	2.5.0 — Other or undefined protocol status	Code 2.5.0 is a general status concerning the protocol needed to pass the message to the next system. It provides no more specific detail, but the leading digit 2 means success, not rejection.	General protocol-related success status without finer detail. Treat as acceptance, not failure: wrong bounce handling harms deliverability metrics. Success class: do not retry. Reputation and list hygiene are unaffected.	{"title":"2.5.0 — Other or undefined protocol status","short_description":"Code 2.5.0 is a general status concerning the protocol needed to pass the message to the next system. It provides no more specific detail, but the leading digit 2 means success, not rejection.","tldr":"General protocol-related success status wit...	["4.5.0","5.5.0","4.5.1","4.5.3"]	esc-2-5-0	indeterminate	unknown	unverified	do_not_retry	no_recommendation	low	true
email-error-2-6-4	2.6.4	X.6.4	https://blazalek.com/en/email-errors/2-6-4	message-content-format	success	do_not_retry	check_context	2.6.4 — Conversion with data loss performed	The message was delivered, but delivery required a conversion in which some data was lost. This is a successful-result warning, not a rejection.	Delivery succeeded after a conversion that lost some data: a success warning, not rejection. Operationally important for content integrity. Do not retry the send. Deliverability stands; reputation is unaffected, but confirm whether partial data loss matters to recipients.	{"title":"2.6.4 — Conversion with data loss performed","short_description":"The message was delivered, but delivery required a conversion in which some data was lost. This is a successful-result warning, not a rejection.","tldr":"Delivery succeeded after a conversion that lost some data: a success warning, not rejectio...	["2.6.8","5.6.3","5.6.6","5.6.7"]	esc-2-6-4	indeterminate	unknown	unverified	do_not_retry	no_recommendation	high	true
email-error-2-6-8	2.6.8	X.6.8	https://blazalek.com/en/email-errors/2-6-8	message-content-format	success	do_not_retry	check_context	2.6.8 — Required UTF-8 reply not permitted by the SMTP client	A reply needed to show the mailbox name would have to contain a UTF-8 string, but the SMTP client does not permit that form of reply. Code 2.6.8 reports this as a success status, not a rejection.	Operationally relevant for mailbox-name display limits. Do not retry. Deliverability and list hygiene are unaffected.	{"title":"2.6.8 — Required UTF-8 reply not permitted by the SMTP client","short_description":"A reply needed to show the mailbox name would have to contain a UTF-8 string, but the SMTP client does not permit that form of reply. Code 2.6.8 reports this as a success status, not a rejection.","tldr":"Operationally relevan...	["5.6.8","2.6.4","5.6.3","5.6.6"]	esc-2-6-8	indeterminate	unknown	unverified	do_not_retry	no_recommendation	medium	true
email-error-2-7-0	2.7.0	X.7.0	https://blazalek.com/en/email-errors/2-7-0	security-authentication-policy	success	do_not_retry	check_context	2.7.0 — Other or undefined security status (success)	The mail system reported a general security-related status that could not be described by a more specific code. The leading digit 2 denotes success, not message rejection.	General security-related success status without a more specific code. Not a failure or rejection: avoid treating it as a bounce. Do not retry. Deliverability is usually unaffected; reputation impact depends on context, not this code alone.	{"title":"2.7.0 — Other or undefined security status (success)","short_description":"The mail system reported a general security-related status that could not be described by a more specific code. The leading digit 2 denotes success, not message rejection.","tldr":"General security-related success status without a more...	["4.7.0","5.7.0","4.7.1","4.7.12"]	esc-2-7-0	indeterminate	unknown	unverified	do_not_retry	no_recommendation	low	true
email-error-4-0-0	4.0.0	X.0.0	https://blazalek.com/en/email-errors/4-0-0	other-undefined	temporary_failure	retry	check_context	Other undefined temporary status	Code 4.0.0 is a general temporary failure: only class 4 is known, with no more specific status. The message may be retried in a controlled way.	Generic temporary failure when only class 4 is known: no finer cause in the response. Operationally prefer controlled retry over list removal. Transient: retry in a controlled way. Unbounded retries add queue noise; reputation harm is unlikely if retry is bounded.	{"title":"Other undefined temporary status","short_description":"Code 4.0.0 is a general temporary failure: only class 4 is known, with no more specific status. The message may be retried in a controlled way.","tldr":"Generic temporary failure when only class 4 is known: no finer cause in the response. Operationally pr...	["2.0.0","5.0.0"]	esc-4-0-0	transient	unknown	unverified	retry_with_backoff	no_recommendation	low	false
email-error-4-1-1	4.1.1	X.1.1	https://blazalek.com/en/email-errors/4-1-1	addressing	temporary_failure	retry	check_context	4.1.1 — Temporary destination mailbox address problem	The receiving system did not find the specified mailbox during this attempt. Because the code begins with 4, this is a temporary failure: delivery may be retried in a controlled way, but the code alone does not yet establish that the address is permanently invalid.	The receiving system did not find the mailbox this attempt: a temporary addressing failure, not yet a hard bounce. Retry in a controlled way after checking the address. Do not remove from lists yet; premature suppression hurts deliverability if the mailbox reappears.	{"title":"4.1.1 — Temporary destination mailbox address problem","short_description":"The receiving system did not find the specified mailbox during this attempt. Because the code begins with 4, this is a temporary failure: delivery may be retried in a controlled way, but the code alone does not yet establish that the ...	["5.1.1","4.1.8","2.1.5","5.1.3"]	esc-4-1-1	transient	recipient_invalid	unverified	retry_with_backoff	no_recommendation	medium	true
email-error-4-1-8	4.1.8	X.1.8	https://blazalek.com/en/email-errors/4-1-8	addressing	temporary_failure	retry	check_context	4.1.8 — Temporary sender system address problem	This attempt reported a problem with the system identified by the sender address. Because the code begins with 4, it is a temporary failure: delivery may be retried in a controlled way, but the sender address and system configuration should be checked first.	Problem with the sender system identified by the From address: a temporary failure. Check sender configuration and DNS before retrying. Transient: controlled retry is appropriate. Repeated failures can affect sender reputation; fix the sender side.	{"title":"4.1.8 — Temporary sender system address problem","short_description":"This attempt reported a problem with the system identified by the sender address. Because the code begins with 4, it is a temporary failure: delivery may be retried in a controlled way, but the sender address and system configuration should...	["5.1.8","4.1.1","2.1.5","5.1.1"]	esc-4-1-8	transient	infrastructure	unverified	retry_after_correction	no_recommendation	high	false
email-error-4-2-0	4.2.0	X.2.0	https://blazalek.com/en/email-errors/4-2-0	mailbox	temporary_failure	retry	check_context	4.2.0 — Recipient mailbox temporarily unavailable (other/undefined mailbox status)	The receiving system reports that the mailbox exists but is temporarily unable to accept the message for an unspecified reason. The code belongs to the temporary class: delivery may succeed on a later attempt.	The recipient mailbox is temporarily unavailable for an unspecified reason: transient, not permanent. Retry with an attempt limit and spacing; do not suppress the address on a single 4.2.0.	{"title":"4.2.0 — Recipient mailbox temporarily unavailable (other/undefined mailbox status)","short_description":"The receiving system reports that the mailbox exists but is temporarily unable to accept the message for an unspecified reason. The code belongs to the temporary class: delivery may succeed on a later atte...	["4.2.4","5.2.2","5.2.3"]	esc-4-2-0	transient	mailbox_state	unverified	retry_with_backoff	no_recommendation	low	false
email-error-4-2-1	4.2.1	X.2.1	https://blazalek.com/en/email-errors/4-2-1	mailbox	temporary_failure	retry	check_context	4.2.1 — Recipient mailbox temporarily not accepting messages (receiving-rate limit)	The receiving system reports that the mailbox exists but is not currently accepting messages, most often because the recipient is receiving mail faster than the system allows. The code belongs to the temporary class: the condition is expected to clear, so delivery may be retried in a controlled way.	The recipient mailbox is temporarily not accepting messages, typically because of a receiving-rate limit rather than a truly disabled account: transient, not permanent. Retry with an attempt limit and spacing; do not suppress the address on a single 4.2.1. If the code persists well past a reasonable window, or a perman...	{"title":"4.2.1 — Recipient mailbox temporarily not accepting messages (receiving-rate limit)","short_description":"The receiving system reports that the mailbox exists but is not currently accepting messages, most often because the recipient is receiving mail faster than the system allows. The code belongs to the temp...	["4.2.4","5.2.2"]	esc-4-2-1	transient	mailbox_state	unverified	retry_with_backoff	no_recommendation	medium	true
email-error-4-2-2	4.2.2	X.2.2	https://blazalek.com/en/email-errors/4-2-2	mailbox	temporary_failure	retry	check_context	4.2.2 — Recipient mailbox temporarily over its storage quota	The receiving system reports that the mailbox is currently over its storage limit and is not accepting messages. The code belongs to the temporary class: the recipient may free up space, so delivery may be retried in a controlled way.	The recipient mailbox is temporarily over its storage quota: transient, not permanent. Retry with an attempt limit and spacing; do not suppress the address on a single 4.2.2. If the code persists well past a reasonable window, or a permanent code such as 5.2.2/5.2.3 appears, treat that as the durable signal instead.	{"title":"4.2.2 — Recipient mailbox temporarily over its storage quota","short_description":"The receiving system reports that the mailbox is currently over its storage limit and is not accepting messages. The code belongs to the temporary class: the recipient may free up space, so delivery may be retried in a controll...	["5.2.2","5.2.3"]	esc-4-2-2	transient	mailbox_state	unverified	retry_with_backoff	no_recommendation	high	false
email-error-4-2-4	4.2.4	X.2.4	https://blazalek.com/en/email-errors/4-2-4	mailbox	temporary_failure	retry	check_context	4.2.4 — Temporary mailing-list expansion problem	The receiving system recognized the destination as a mailing list but could not expand it to recipients during this attempt. The code belongs to the temporary class, so delivery may be retried in a controlled way.	The destination is a mailing list that could not be expanded this attempt: temporary, not permanent. Retry in a controlled way; do not treat as a hard bounce. List hygiene: hold suppressions until expansion succeeds or a permanent code appears.	{"title":"4.2.4 — Temporary mailing-list expansion problem","short_description":"The receiving system recognized the destination as a mailing list but could not expand it to recipients during this attempt. The code belongs to the temporary class, so delivery may be retried in a controlled way.","tldr":"The destination ...	["5.2.2","5.2.3"]	esc-4-2-4	transient	mailbox_state	unverified	retry_with_backoff	no_recommendation	medium	false
email-error-4-3-0	4.3.0	X.3.0	https://blazalek.com/en/email-errors/4-3-0	mail-system	temporary_failure	retry	check_context	4.3.0 — Other or undefined temporary mail-system status	The destination system exists and normally accepts mail, but a general problem in that system prevented delivery during this attempt. The leading digit 4 denotes a temporary failure, so delivery may be retried in a controlled way.	The destination mail system had a general problem preventing delivery this attempt: temporary failure without finer detail. Controlled retry is appropriate. Usually no lasting reputation hit; short-term queue impact only if retries are unbounded.	{"title":"4.3.0 — Other or undefined temporary mail-system status","short_description":"The destination system exists and normally accepts mail, but a general problem in that system prevented delivery during this attempt. The leading digit 4 denotes a temporary failure, so delivery may be retried in a controlled way.",...	["2.3.0","5.3.0","4.3.1","4.3.2"]	esc-4-3-0	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	low	false
email-error-4-3-1	4.3.1	X.3.1	https://blazalek.com/en/email-errors/4-3-1	mail-system	temporary_failure	retry	check_context	4.3.1 — Temporarily full mail system	The mail system exceeded its available storage during this attempt. This is a system-wide resource problem, so an individual recipient may be unable to free space on their own. Because the code begins with 4, delivery may be retried in a controlled way.	The mail system ran out of storage during this attempt: a system-wide temporary resource limit. Retry in a controlled way; the recipient alone may not fix it. Not a hard bounce; premature list removal hurts deliverability when space frees up.	{"title":"4.3.1 — Temporarily full mail system","short_description":"The mail system exceeded its available storage during this attempt. This is a system-wide resource problem, so an individual recipient may be unable to free space on their own. Because the code begins with 4, delivery may be retried in a controlled wa...	["4.3.0","4.3.2","2.3.0","2.3.6"]	esc-4-3-1	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	high	false
email-error-4-3-2	4.3.2	X.3.2	https://blazalek.com/en/email-errors/4-3-2	mail-system	temporary_failure	retry	check_context	4.3.2 — System temporarily not accepting network messages	The host on which the recipient's mailbox resides is not currently accepting messages. Because the code begins with 4, this is a temporary failure and delivery may be retried in a controlled way.	The recipient's host is not accepting messages right now: a transient mail-system condition. Controlled retry is appropriate. Not a permanent rejection or hard bounce; avoid list suppression until a permanent code confirms the address is bad.	{"title":"4.3.2 — System temporarily not accepting network messages","short_description":"The host on which the recipient's mailbox resides is not currently accepting messages. Because the code begins with 4, this is a temporary failure and delivery may be retried in a controlled way.","tldr":"The recipient's host is n...	["5.3.2","4.3.0","4.3.1","2.3.0"]	esc-4-3-2	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	high	false
email-error-4-4-0	4.4.0	X.4.0	https://blazalek.com/en/email-errors/4-4-0	network-dns-routing	temporary_failure	retry	check_context	4.4.0 — Temporary failure for an unspecified network or routing reason (other/undefined network status)	The receiving system reports a temporary failure using the generic "other or undefined network or routing status" code: some network-layer or routing/replication condition prevented delivery at this attempt, but the response does not identify one of the more specific network conditions this catalog also tracks (no answ...	Mail failed temporarily for an unspecified network or routing reason: transient, not permanent. Retry with an attempt limit and spacing; do not suppress the address on a single 4.4.0. The pattern is an explicit catch-all, so do not assume one cause (DNS lookup, replication) without checking the response text.	{"title":"4.4.0 — Temporary failure for an unspecified network or routing reason (other/undefined network status)","short_description":"The receiving system reports a temporary failure using the generic \"other or undefined network or routing status\" code: some network-layer or routing/replication condition prevented ...	["4.4.1","4.4.5","5.4.0"]	esc-4-4-0	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	low	false
email-error-4-4-1	4.4.1	X.4.1	https://blazalek.com/en/email-errors/4-4-1	network-dns-routing	temporary_failure	retry	check_context	4.4.1 — No answer from remote host	An outbound connection attempt received no answer from the remote system. The standard indicates that the system may have been busy or unable to accept a connection. The code belongs to the temporary class, so delivery may be retried in a controlled way.	Outbound connection got no response from the remote host: a transient network/routing failure. Retry in a controlled way after checking connectivity and DNS. Usually no lasting deliverability or reputation harm if retries stay bounded.	{"title":"4.4.1 — No answer from remote host","short_description":"An outbound connection attempt received no answer from the remote system. The standard indicates that the system may have been busy or unable to accept a connection. The code belongs to the temporary class, so delivery may be retried in a controlled way...	["4.4.2","4.4.3","4.4.5","5.4.3"]	esc-4-4-1	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	high	false
email-error-4-4-2	4.4.2	X.4.2	https://blazalek.com/en/email-errors/4-4-2	network-dns-routing	temporary_failure	retry	check_context	4.4.2 — Bad connection	An outbound connection was established, but the message transaction could not be completed over it. The standard points to a timeout or inadequate connection quality. The code belongs to the temporary class, so delivery may be retried in a controlled way.	A connection was made but the message transaction could not complete: temporary network quality or timeout issue. Controlled retry is appropriate. Unbounded retries add queue load; reputation impact is usually short-lived if delivery eventually succeeds.	{"title":"4.4.2 — Bad connection","short_description":"An outbound connection was established, but the message transaction could not be completed over it. The standard points to a timeout or inadequate connection quality. The code belongs to the temporary class, so delivery may be retried in a controlled way.","tldr":"...	["4.4.1","4.4.3","4.4.5","5.4.3"]	esc-4-4-2	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	high	false
email-error-4-4-3	4.4.3	X.4.3	https://blazalek.com/en/email-errors/4-4-3	network-dns-routing	temporary_failure	retry	check_context	4.4.3 — Directory server failure	The network system could not forward the message because a directory server was unavailable. Inability to connect to an Internet DNS server is one standards example, but the code alone does not establish that the problem involved DNS. The code belongs to the temporary class, so delivery may be retried in a controlled w...	Message forwarding failed because a directory server was unavailable: a transient routing failure. Retry in a controlled way after checking DNS/directory services. Usually no lasting reputation hit; deliverability recovers when the directory responds again.	{"title":"4.4.3 — Directory server failure","short_description":"The network system could not forward the message because a directory server was unavailable. Inability to connect to an Internet DNS server is one standards example, but the code alone does not establish that the problem involved DNS. The code belongs to ...	["5.4.3","4.4.1","4.4.2","4.4.5"]	esc-4-4-3	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	high	false
email-error-4-4-5	4.4.5	X.4.5	https://blazalek.com/en/email-errors/4-4-5	network-dns-routing	temporary_failure	retry	check_context	4.4.5 — Mail system congestion	A mail system could not deliver the message because it was congested. The code does not identify which system or party is responsible for that condition. It belongs to the temporary class, so delivery may be retried in a controlled way.	Delivery failed because a mail system was congested: a temporary capacity condition. Controlled retry is appropriate once load eases. Not a hard bounce; suppressing addresses prematurely risks unnecessary list hygiene loss.	{"title":"4.4.5 — Mail system congestion","short_description":"A mail system could not deliver the message because it was congested. The code does not identify which system or party is responsible for that condition. It belongs to the temporary class, so delivery may be retried in a controlled way.","tldr":"Delivery fa...	["4.4.1","4.4.2","4.4.3","5.4.3"]	esc-4-4-5	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	medium	true
email-error-4-4-6	4.4.6	X.4.6	https://blazalek.com/en/email-errors/4-4-6	network-dns-routing	temporary_failure	retry	check_context	4.4.6 — Routing loop detected between mail systems	The sending or an intermediate mail system reports that this message was forwarded from system to system too many times without reaching its destination — a routing loop. The code belongs to the temporary class: once whichever forwarding rule or routing table is causing the loop gets fixed, delivery may succeed, so ret...	4.4.6 means a routing loop bounced this message between mail systems past the accepted hop limit: temporary in principle, but only if someone actually breaks the loop. Retry a bounded number of times while the forwarding rule or routing-table misconfiguration gets traced and fixed; if the condition persists past a reas...	{"title":"4.4.6 — Routing loop detected between mail systems","short_description":"The sending or an intermediate mail system reports that this message was forwarded from system to system too many times without reaching its destination — a routing loop. The code belongs to the temporary class: once whichever forwarding...	["4.4.1","4.4.5","5.4.0","5.4.6"]	esc-4-4-6	transient	infrastructure	unverified	retry_after_correction	no_recommendation	medium	true
email-error-4-5-0	4.5.0	X.5.0	https://blazalek.com/en/email-errors/4-5-0	delivery-protocol	temporary_failure	retry	check_context	4.5.0 — Other or undefined temporary protocol status	A problem occurred with the protocol needed to pass the message to the next system, but no other detail code described it adequately. The leading digit 4 makes this a temporary result, so delivery may be retried in a controlled way.	A protocol problem occurred while passing the message on: temporary failure without a more specific code. Check SMTP logs, then retry in a controlled way. Transient: unbounded retries add noise; deliverability impact is usually short-term.	{"title":"4.5.0 — Other or undefined temporary protocol status","short_description":"A problem occurred with the protocol needed to pass the message to the next system, but no other detail code described it adequately. The leading digit 4 makes this a temporary result, so delivery may be retried in a controlled way.","...	["2.5.0","5.5.0","4.5.1","4.5.3"]	esc-4-5-0	transient	infrastructure	unverified	retry_with_backoff	no_recommendation	low	false
email-error-4-5-1	4.5.1	X.5.1	https://blazalek.com/en/email-errors/4-5-1	delivery-protocol	temporary_failure	retry	check_context	4.5.1 — Temporarily invalid protocol command	A mail system rejected a protocol command because it was issued out of sequence or was unsupported. The leading digit 4 classifies this concrete result as temporary, so delivery may be retried in a controlled way after the command context is checked.	A protocol command was rejected as out of sequence or unsupported: classified temporary in this response. Inspect the SMTP transaction, then retry in a controlled way. Fixing the command order protects deliverability; reputation harm is unlikely if corrected.	{"title":"4.5.1 — Temporarily invalid protocol command","short_description":"A mail system rejected a protocol command because it was issued out of sequence or was unsupported. The leading digit 4 classifies this concrete result as temporary, so delivery may be retried in a controlled way after the command context is c...	["5.5.1","4.5.0","4.5.3","4.5.4"]	esc-4-5-1	transient	infrastructure	unverified	retry_after_correction	no_recommendation	medium	false
email-error-4-5-3	4.5.3	X.5.3	https://blazalek.com/en/email-errors/4-5-3	delivery-protocol	temporary_failure	retry	check_context	4.5.3 — Too many recipients	One message specified more recipients than the protocol could handle in that attempt. The code belongs to the temporary class; normally, the remaining recipients should be separated and delivery to them retried in a controlled way.	Too many recipients were specified for one message in this attempt: a temporary protocol limit. Split remaining recipients and retry in a controlled way. Not a bounce for valid addresses; list hygiene should follow actual permanent failures, not this code alone.	{"title":"4.5.3 — Too many recipients","short_description":"One message specified more recipients than the protocol could handle in that attempt. The code belongs to the temporary class; normally, the remaining recipients should be separated and delivery to them retried in a controlled way.","tldr":"Too many recipients...	["4.5.0","4.5.1","4.5.4","2.5.0"]	esc-4-5-3	transient	rate_limited	unverified	retry_after_correction	no_recommendation	medium	true
email-error-4-5-4	4.5.4	X.5.4	https://blazalek.com/en/email-errors/4-5-4	delivery-protocol	temporary_failure	retry	check_context	4.5.4 — Temporarily invalid command arguments	A mail system recognized the command but rejected its arguments as invalid. The leading digit 4 classifies this concrete result as temporary, so delivery may be retried in a controlled way after the arguments are checked and, when necessary, corrected.	The mail system rejected command arguments as invalid: temporary in this response. Correct the arguments, then retry in a controlled way. Transient protocol issue; deliverability and reputation are usually unaffected once arguments are fixed.	{"title":"4.5.4 — Temporarily invalid command arguments","short_description":"A mail system recognized the command but rejected its arguments as invalid. The leading digit 4 classifies this concrete result as temporary, so delivery may be retried in a controlled way after the arguments are checked and, when necessary, ...	["5.5.4","4.5.0","4.5.1","4.5.3"]	esc-4-5-4	transient	infrastructure	unverified	retry_after_correction	no_recommendation	medium	false
email-error-4-7-0	4.7.0	X.7.0	https://blazalek.com/en/email-errors/4-7-0	security-authentication-policy	temporary_failure	retry	check_context	4.7.0 — Other or undefined temporary security status	The message was returned because of a security-related problem, but the response does not describe it more precisely. The leading digit 4 denotes a temporary failure, so delivery may be retried in a controlled way.	The message was returned for an unspecified security-related reason: a temporary failure. Investigate auth/policy context, then retry in a controlled way. Unresolved repeats can signal reputation risk; do not treat as a hard bounce without a permanent code.	{"title":"4.7.0 — Other or undefined temporary security status","short_description":"The message was returned because of a security-related problem, but the response does not describe it more precisely. The leading digit 4 denotes a temporary failure, so delivery may be retried in a controlled way.","tldr":"The message...	["2.7.0","5.7.0","4.7.1","4.7.12"]	esc-4-7-0	transient	policy_block	unverified	retry_with_backoff	no_recommendation	low	false
email-error-4-7-1	4.7.1	X.7.1	https://blazalek.com/en/email-errors/4-7-1	security-authentication-policy	temporary_failure	retry	check_context	4.7.1 — Delivery not authorized, message temporarily refused	The system refused the current attempt because the sender was not authorized to send to the destination. The decision may result from per-host or per-recipient filtering. The leading digit 4 denotes a temporary failure, so delivery may be retried in a controlled way.	The sender was not authorized to deliver to this destination: a temporary filtering or policy block. Fix authorization or alignment, then retry in a controlled way. Repeated blocks can hurt sender reputation; not a hard bounce for the recipient address itself.	{"title":"4.7.1 — Delivery not authorized, message temporarily refused","short_description":"The system refused the current attempt because the sender was not authorized to send to the destination. The decision may result from per-host or per-recipient filtering. The leading digit 4 denotes a temporary failure, so deli...	["5.7.1","4.7.0","4.7.12","4.7.15"]	esc-4-7-1	transient	policy_block	unverified	retry_after_correction	no_recommendation	medium	true
email-error-4-7-12	4.7.12	X.7.12	https://blazalek.com/en/email-errors/4-7-12	security-authentication-policy	temporary_failure	retry	check_context	4.7.12 — Authentication mechanism transition required	The server replied to the AUTH command that the user must first transition to the selected authentication mechanism. The leading digit 4 denotes a temporary failure, so a controlled attempt may be made after the required transition is completed safely.	SMTP AUTH failed because the account must first switch to a required authentication mechanism. Fix auth configuration before resubmitting mail; this is an operational gate, not a recipient deliverability signal. Temporary failure: retry with backoff only after the approved mechanism transition.	{"title":"4.7.12 — Authentication mechanism transition required","short_description":"The server replied to the AUTH command that the user must first transition to the selected authentication mechanism. The leading digit 4 denotes a temporary failure, so a controlled attempt may be made after the required transition is...	["4.7.0","4.7.1","4.7.15","4.7.16"]	esc-4-7-12	transient	authentication_failure	unverified	retry_after_correction	no_recommendation	high	false
email-error-4-7-15	4.7.15	X.7.15	https://blazalek.com/en/email-errors/4-7-15	security-authentication-policy	temporary_failure	retry	check_context	4.7.15 — Priority level is too low	The receiving SMTP server did not accept the message because the specified priority level was below the lowest level the server currently accepts. The leading digit 4 denotes a temporary failure, so a controlled retry is appropriate.	The receiving server refused the message because its declared priority was below the minimum it currently accepts. Important for bulk or low-priority traffic scheduling, not list hygiene. Temporary: retry later or adjust priority if your path supports it; no lasting reputation hit if retries stay bounded.	{"title":"4.7.15 — Priority level is too low","short_description":"The receiving SMTP server did not accept the message because the specified priority level was below the lowest level the server currently accepts. The leading digit 4 denotes a temporary failure, so a controlled retry is appropriate.","tldr":"The receiv...	["5.7.15","4.7.0","4.7.1","4.7.12"]	esc-4-7-15	transient	policy_block	unverified	retry_with_backoff	no_recommendation	high	false
email-error-4-7-16	4.7.16	X.7.16	https://blazalek.com/en/email-errors/4-7-16	security-authentication-policy	temporary_failure	retry	check_context	4.7.16 — Message too big for the specified priority	The server temporarily rejected the message because it is too big for the specified priority. A controlled retry may be made after the condition clears.	The server temporarily rejected the message because it exceeds the size allowed for its priority level. Size and priority settings matter for throughput, not recipient list quality. Temporary failure: retry after the condition clears or with a smaller message or higher priority where supported.	{"title":"4.7.16 — Message too big for the specified priority","short_description":"The server temporarily rejected the message because it is too big for the specified priority. A controlled retry may be made after the condition clears.","tldr":"The server temporarily rejected the message because it exceeds the size al...	["5.7.16","4.7.0","4.7.1","4.7.12"]	esc-4-7-16	transient	policy_block	unverified	retry_after_correction	no_recommendation	medium	true

End of preview. Expand in Data Studio

Open SMTP Error Dataset

Open SMTP Error Dataset is an English-language, machine-readable reference package for SMTP enhanced-status knowledge and cautious operational classification. Version 1.1.0 contains 92 stable knowledge records and a separate, auditable catalog of 120 classification rules.

The package is a reference artifact, not a live provider-policy feed. It helps with observability, support, parser testing, and bounded delivery operations; it does not establish recipient state or final inbox placement.

Configurations and contracts

Concern	Location	Contract
Knowledge data	default configuration	92 English knowledge records, including diagnostic and delivery-decision context.
Bounce recognition	data/bounce-recognition-rules.json	Stable 1.0.0 recognizer contract: 92 exact enhanced-status mappings and four text signals.
Operational classification	classification_rules configuration	120 ordered rules: 99 exact mappings and 21 cautious fallbacks.

The default configuration is the knowledge dataset. The classification_rules configuration is a distinct rule catalog for applications that need an explicit decision order. Do not treat either configuration as a claim about a current provider policy.

Knowledge classification fields

Each knowledge record includes these operational_classification fields:

rule_key
failure_persistence
cause_family
recipient_validity
retry_disposition
suppression_disposition
confidence
needs_review

The first matching classification rule is represented by rule_key. A needs_review value of true means the result is suitable for human review or additional context gathering, not an irreversible automated action.

Classification-rule schema

Each row in the classification_rules configuration has these public fields:

schema_version
rule_key
source
precedence_tier
enhanced_status_code
enhanced_status_prefix
match_field
match_operator
match_value
failure_persistence
cause_family
recipient_validity
retry_disposition
suppression_disposition
confidence
needs_review
rationale
source_title
evidence_reference
knowledge_record_id
excluded_enhanced_status_codes

Rule evaluation is deterministic: exact mappings are considered first, exclusions are honored before fallbacks, then cautious fallback rules are considered. Results outside that coverage remain unclassified. In particular, 5.7.28 is intentionally unclassified by policy, while the exact mapping for 4.7.28 remains available.

Load both configurations

from datasets import load_dataset

knowledge = load_dataset(
    "blazalek/open-smtp-error-dataset",
    split="train",
)
rules = load_dataset(
    "blazalek/open-smtp-error-dataset",
    "classification_rules",
    split="train",
)

Use the knowledge configuration for explanatory catalog content. Use the rule configuration when an application needs to show its rule source, precedence, confidence, and review requirement.

Public boundary and responsible use

Raw SMTP responses, observed delivery-event examples, recipient information, personal data, provider-specific wire text, and internal working material are excluded from this release. The public package contains privacy-safe structured knowledge, rules, and provenance only.

Do not use a text-only signal or a result marked needs_review to automatically suppress a recipient, close an investigation, or make another irreversible delivery decision. Keep operational telemetry in the system authorized to hold it.

Public files

The proposed local v1.1.0 base payload contains:

README.md
bounce-recognition-guide.md
CHANGELOG.md
NOTICE.md
data/open-smtp-error-knowledge.jsonl
data/open-smtp-error-knowledge.csv
data/open-smtp-error-knowledge.parquet
data/bounce-recognition-rules.json
data/dataset-manifest.json
data/dataset.schema.json
data/classification-rules.jsonl
data/classification-rules.csv
data/classification-rules.parquet
data/classification-rule.schema.json

LICENSE.md is deliberately absent until its identifier and treatment receive a separate owner decision. The NOTICE file records third-party attribution; it does not state a licence for the overall dataset.

See CHANGELOG.md for version history and bounce-recognition-guide.md for the recognizer's separate integration contract.

Downloads last month: 75