Incoming.email

Incoming.email is in development.

For now, visit our sister site Outgoing.email for practical information and tips on optimising outgoing mail flows, deliverability, sender reputation, authentication, and email infrastructure.

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Standards reference

RFCs for incoming email, mailboxes, and filtering.

The RFCs below are useful starting points for understanding the standards behind inbound SMTP, MX routing, IMAP, POP3, authentication checks, abuse reporting, MIME, and common filtering signals.

SMTP, MX, and incoming delivery

Core transport and DNS documents for moving messages between mail servers and finding the right receiving host.

RFC 5321

Simple Mail Transfer Protocol

RFC 5322

Internet Message Format

RFC 1035

Domain Names - Implementation and Specification

RFC 974

Mail Routing and the Domain System

RFC 3207

SMTP Service Extension for Secure SMTP over TLS

RFC 3463

Enhanced Mail System Status Codes

RFC 3464

Delivery Status Notifications

IMAP and mailbox access

Specifications for server-side mailboxes, message flags, folders, synchronisation, and client access.

RFC 9051

Internet Message Access Protocol - Version 4rev2

RFC 3501

Internet Message Access Protocol - Version 4rev1

RFC 2177

IMAP4 IDLE command

RFC 6851

IMAP MOVE Extension

RFC 4315

IMAP UIDPLUS Extension

POP3 retrieval

Documents for simple mailbox download, POP3 extensions, service discovery, and modern TLS expectations.

RFC 1939

Post Office Protocol - Version 3

RFC 2449

POP3 Extension Mechanism

RFC 6186

Use of SRV Records for Locating Email Submission and Access Services

RFC 8314

Cleartext Considered Obsolete for Email Submission and Access

Authentication and filtering signals

Common standards used by receiving systems when evaluating trust, alignment, authentication, and reporting.

RFC 7208

Sender Policy Framework (SPF)

RFC 6376

DomainKeys Identified Mail (DKIM) Signatures

RFC 7489

Domain-based Message Authentication, Reporting, and Conformance (DMARC)

RFC 8601

Authentication-Results Message Header Field

RFC 8617

Authenticated Received Chain (ARC)

RFC 5965

Abuse Reporting Format

Message content and mailbox handling

Related documents for message bodies, MIME structure, list headers, and server-side filtering rules.

RFC 2045

MIME Part One: Format of Internet Message Bodies

RFC 2046

MIME Part Two: Media Types

RFC 2369

Use of URLs as Meta-Syntax for Core Mail List Commands

RFC 8058

Signaling One-Click Functionality for List Email Headers

RFC 5228

Sieve: An Email Filtering Language

Related pages

MX

A plain-English guide to MX records, mail exchanger priority, DNS lookups, fallback hosts, and how senders find receiving mail servers. [read more]

SMTP

How inbound SMTP works: connection, greeting, envelope sender, recipients, DATA, acceptance, rejection, deferrals, and receiving server policy. [read more]

IMAP

A practical introduction to IMAP, mailbox folders, message state, sync, search, flags, and how mail clients read messages after delivery. [read more]

POP3

A guide to POP3, message download, mailbox retrieval, deletion behavior, limitations, and how it differs from IMAP. [read more]

Filtering

How inbound email filtering uses authentication, reputation, rate limits, spam scoring, malware checks, and policy to decide what reaches the inbox. [read more]

Disclaimer

Basic disclaimer for Incoming.email, an informational resource about inbound email, mail protocols, delivery, filtering, and infrastructure. [read more]