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RFC decoded

What each email RFC actually requires, and which one you should be reading. 99 current documents, with the 28 that are current but amended by something later, and the normative requirements pulled out section by section.

A number, a name, or what you are trying to do 99 current email RFCs, resolved against the RFC Editor index

Try 821 and 7489 are numbers people are still handed. Both have been replaced.

Every current email RFC

Grouped the way you look for them rather than by number. 77 replaced documents resolve to whatever took their place, so an old number still finds the right answer.

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Transport

1870SMTP Service Extension for Message Size DeclarationInternet Standard1 2034SMTP Service Extension for Returning Enhanced Error CodesProposed Standard1 2920SMTP Service Extension for Command PipeliningInternet Standard18 3030SMTP Service Extensions for Transmission of Large and Binary MIME MessagesProposed Standard27 3461Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs)Draft Standard109 3463Enhanced Mail System Status CodesDraft Standard1 3464An Extensible Message Format for Delivery Status NotificationsDraft Standard40 3885SMTP Service Extension for Message TrackingProposed Standard22 3886An Extensible Message Format for Message Tracking ResponsesProposed Standard15 4468Message Submission BURL ExtensionProposed Standard18 4865SMTP Submission Service Extension for Future Message ReleaseProposed Standard28 5321Simple Mail Transfer ProtocolDraft Standard360 6152SMTP Service Extension for 8-bit MIME TransportInternet Standard 6522The Multipart/Report Media Type for the Reporting of Mail System Administrative MessagesInternet Standard11 6531SMTP Extension for Internationalized EmailProposed Standard41 6710Simple Mail Transfer Protocol Extension for Message Transfer PrioritiesProposed Standard26 7504SMTP 521 and 556 Reply CodesProposed Standard4 7505A "Null MX" No Service Resource Record for Domains That Accept No MailProposed Standard4

Message format

2045Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message BodiesDraft Standard6 2046Multipurpose Internet Mail Extensions (MIME) Part Two: Media TypesDraft Standard11 2047MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII TextDraft Standard20 2049Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and ExamplesDraft Standard3 2183Communicating Presentation Information in Internet Messages: The Content-Disposition Header FieldProposed Standard12 2231MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and ContinuationsProposed Standard10 2387The MIME Multipart/Related Content-typeProposed Standard 2392Content-ID and Message-ID Uniform Resource LocatorsProposed Standard 2557MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)Proposed Standard31 3676The Text/Plain Format and DelSp ParametersProposed Standard31 4289Multipurpose Internet Mail Extensions (MIME) Part Four: Registration ProceduresBest Current Practice24 5147URI Fragment Identifiers for the text/plain Media TypeProposed Standard20 5322Internet Message FormatDraft Standard64 5536Netnews Article FormatProposed Standard54 5537Netnews Architecture and ProtocolsProposed Standard211 6657Update to MIME regarding "charset" Parameter Handling in Textual Media TypesProposed Standard7 6838Media Type Specifications and Registration ProceduresBest Current Practice61 6854Update to Internet Message Format to Allow Group Syntax in the "From:" and "Sender:" Header FieldsProposed Standard9 8098Message Disposition NotificationInternet Standard57 8315Cancel-Locks in Netnews ArticlesProposed Standard26 9057Email Author Header FieldExperimental3 9694Guidelines for the Definition of New Top-Level Media TypesBest Current Practice10

Authentication

5863DomainKeys Identified Mail (DKIM) Development, Deployment, and OperationsInformational2 6008Authentication-Results Registration for Differentiating among Cryptographic ResultsProposed Standard4 6376DomainKeys Identified Mail (DKIM) SignaturesInternet Standard217 6377DomainKeys Identified Mail (DKIM) and Mailing ListsBest Current Practice36 6541DomainKeys Identified Mail (DKIM) Authorized Third-Party SignaturesExperimental22 7208Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1Proposed Standard67 7372Email Authentication Status CodesProposed Standard1 7960Interoperability Issues between Domain-based Message Authentication, Reporting, and Conformance (DMARC) and Indirect Email FlowsInformational 8301Cryptographic Algorithm and Key Usage Update to DomainKeys Identified Mail (DKIM)Proposed Standard8 8463A New Cryptographic Signature Method for DomainKeys Identified Mail (DKIM)Proposed Standard1 8553DNS Attrleaf Changes: Fixing Specifications That Use Underscored Node NamesBest Current Practice2 8601Message Header Field for Indicating Message Authentication StatusProposed Standard39 8616Email Authentication for Internationalized MailProposed Standard6 8617The Authenticated Received Chain (ARC) ProtocolExperimental24 9989Domain-Based Message Authentication, Reporting, and Conformance (DMARC)Proposed Standard80 9990Domain-Based Message Authentication, Reporting, and Conformance (DMARC) Aggregate ReportingProposed Standard56 9991Domain-Based Message Authentication, Reporting, and Conformance (DMARC) Failure ReportingProposed Standard14

Transport security

3207SMTP Service Extension for Secure SMTP over Transport Layer SecurityProposed Standard20 7672SMTP Security via Opportunistic DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS)Proposed Standard83 7817Updated Transport Layer Security (TLS) Server Identity Check Procedure for Email-Related ProtocolsProposed Standard22 8314Cleartext Considered Obsolete: Use of Transport Layer Security (TLS) for Email Submission and AccessProposed Standard82 8460SMTP TLS ReportingProposed Standard42 8461SMTP MTA Strict Transport Security (MTA-STS)Proposed Standard51 8689SMTP Require TLS OptionProposed Standard36 8997Deprecation of TLS 1.1 for Email Submission and AccessProposed Standard12

Internationalization

6530Overview and Framework for Internationalized EmailProposed Standard16 6532Internationalized Email HeadersProposed Standard10 6533Internationalized Delivery Status and Disposition NotificationsProposed Standard31 6856Post Office Protocol Version 3 (POP3) Support for UTF-8Proposed Standard18 6857Post-Delivery Message Downgrading for Internationalized Email MessagesProposed Standard5 6858Simplified POP and IMAP Downgrading for Internationalized EmailProposed Standard 9755IMAP Support for UTF-8Proposed Standard17

Submission and access

1939Post Office Protocol - Version 3Internet Standard7 1957Some Observations on Implementations of the Post Office Protocol (POP3)Informational 2449POP3 Extension MechanismProposed Standard31 4954SMTP Service Extension for AuthenticationProposed Standard67 5248A Registry for SMTP Enhanced Mail System Status CodesBest Current Practice 6186Use of SRV Records for Locating Email Submission/Access ServicesProposed Standard25 6409Message Submission for MailInternet Standard42 8437IMAP UNAUTHENTICATE Extension for Connection ReuseProposed Standard6 9051Internet Message Access Protocol (IMAP) - Version 4rev2Proposed Standard413

Reporting and feedback

2369The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header FieldsProposed Standard20 2919List-Id: A Structured Field and Namespace for the Identification of Mailing ListsProposed Standard21 5965An Extensible Format for Email Feedback ReportsProposed Standard36 6449Complaint Feedback Loop Operational RecommendationsInformational 6591Authentication Failure Reporting Using the Abuse Reporting FormatProposed Standard20 6650Creation and Use of Email Feedback Reports: An Applicability Statement for the Abuse Reporting Format (ARF)Proposed Standard35 6692Source Ports in Abuse Reporting Format (ARF) ReportsProposed Standard4 8058Signaling One-Click Functionality for List Email HeadersProposed Standard16

Anti-abuse and operations

2142Mailbox Names for Common Services, Roles and FunctionsProposed Standard2 5068Email Submission Operations: Access and Accountability RequirementsBest Current Practice18 5782DNS Blacklists and WhitelistsInformational29 6471Overview of Best Email DNS-Based List (DNSBL) Operational PracticesInformational93 6647Email Greylisting: An Applicability Statement for SMTPProposed Standard12

Architecture

1123Requirements for Internet Hosts - Application and SupportInternet Standard239 2181Clarifications to the DNS SpecificationProposed Standard1 5598Internet Mail ArchitectureInformational 7766DNS Transport over TCP - Implementation RequirementsProposed Standard44 9210DNS Transport over TCP - Operational RequirementsBest Current Practice39

Where this comes from

The metadata is parsed from the RFC Editor's index, which is what records status, what a document replaced, and what has amended it since. The requirements are extracted from the RFC text itself: every sentence carrying an RFC 2119 keyword, with the section it came from. Only the uppercase keywords count, because a lowercase "must" is prose and binds nobody.