# The Email Specification

> A platform-agnostic specification of what reliable, accessible, secure email does.

## Specification pages

- [About the platform-agnostic email spec · Email Spec](https://specification.email/about/): Learn how The Email Specification turns scattered RFCs, accessibility guidance, and provider requirements into one testable, open checklist.
- [Email specification changelog · Email Spec](https://specification.email/changelog/): Follow additions, status changes, and corrections across The Email Specification’s sourced requirements and machine-readable outputs.
- [Email quality and compliance checklist · Email Spec](https://specification.email/checklist/): Audit a delivered email and its sending domain against sourced requirements for authentication, accessibility, security, privacy, and rendering.
- [Email standards considered but excluded · Email Spec](https://specification.email/considered/): See which email technologies were evaluated for The Email Specification, why they remain outside the core, and what would trigger a review.
- [Email standards for better messages · Email Spec](https://specification.email/): Build reliable email with sourced guidance for authentication, deliverability, accessibility, privacy, security, and client rendering.
- [MCP server for email standards · Email Spec](https://specification.email/mcp/): Connect an AI agent to the read-only Email Specification MCP server for search, topic retrieval, filtered lists, checklists, and change tracking.
- [Search email standards and requirements · Email Spec](https://specification.email/search/): Search every topic in The Email Specification, including RFC-backed guidance for authentication, deliverability, rendering, privacy, and accessibility.
- [Email color contrast and cues · Email Spec](https://specification.email/spec/accessibility/color-and-contrast/): Text, controls, and meaningful graphics need sufficient contrast, and color must never be the only way the message communicates state.
- [Alternative text for email images · Email Spec](https://specification.email/spec/accessibility/image-alt-text/): Every informative image needs concise equivalent alt text, while decorative images need an empty alt attribute and no repeated meaning.
- [Accessibility email requirements · Email Spec](https://specification.email/spec/accessibility/): Readable, operable messages for people of all abilities. Browse 3 sourced, testable requirements in The Email Specification.
- [Semantic email structure · Email Spec](https://specification.email/spec/accessibility/semantic-structure/): Use headings, paragraphs, lists, tables, and landmarks according to meaning so assistive technology can navigate the message.
- [DomainKeys Identified Mail signatures · Email Spec](https://specification.email/spec/authentication/dkim-signatures/): Sign outgoing mail with DKIM using aligned domains, protected private keys, rotating selectors, and canonicalization that survives normal transit.
- [DMARC alignment and policy · Email Spec](https://specification.email/spec/authentication/dmarc-policy/): Publish DMARC, collect reports, align SPF or DKIM with the visible From domain, and move to enforcement only after legitimate flows pass.
- [Authentication email requirements · Email Spec](https://specification.email/spec/authentication/): SPF, DKIM, DMARC, transport security, and domain trust. Browse 3 sourced, testable requirements in The Email Specification.
- [Sender Policy Framework (SPF) · Email Spec](https://specification.email/spec/authentication/sender-policy-framework/): Publish one bounded SPF policy that authorizes legitimate envelope senders without exceeding DNS lookup limits or permitting the world.
- [Safe and usable email attachments · Email Spec](https://specification.email/spec/automation/attachments/): Attach only necessary files with accurate media types, safe names, bounded size, malware controls, and an accessible alternative where possible.
- [Calendar invitation interoperability · Email Spec](https://specification.email/spec/automation/calendar-invitations/): Calendar mail must include valid iCalendar data, stable event identifiers, correct methods, time zones, and updates that replace prior versions.
- [Automation email requirements · Email Spec](https://specification.email/spec/automation/): Machine-readable actions, calendars, receipts, and agent use. Browse 3 sourced, testable requirements in The Email Specification.
- [Machine-readable email actions · Email Spec](https://specification.email/spec/automation/machine-readable-actions/): Add structured actions only as progressive enhancement, bind them to visible content, and keep the ordinary website workflow complete.
- [Spam complaint handling · Email Spec](https://specification.email/spec/deliverability/complaint-handling/): Subscribe to available feedback loops, connect complaints to recipients safely, suppress them promptly, and monitor complaint rates by message stream.
- [Deliverability email requirements · Email Spec](https://specification.email/spec/deliverability/): Reputation, list quality, bounces, and inbox placement. Browse 3 sourced, testable requirements in The Email Specification.
- [Recipient list hygiene · Email Spec](https://specification.email/spec/deliverability/list-hygiene/): Send only to expected recipients, remove permanent failures, suppress complainers, and stop mailing addresses that never engage or consent.
- [Reverse DNS and sending identity · Email Spec](https://specification.email/spec/deliverability/reverse-dns/): Every sending IP needs stable forward-confirmed reverse DNS, an SMTP greeting that matches it, and an operational domain identity.
- [Required message header fields · Email Spec](https://specification.email/spec/foundations/header-fields/): Each message needs a valid Date, From, and globally unique Message-ID, with recipient and subject fields that match its purpose.
- [Foundations email requirements · Email Spec](https://specification.email/spec/foundations/): Message format, headers, MIME, identity, and the envelope. Browse 3 sourced, testable requirements in The Email Specification.
- [Internet message format · Email Spec](https://specification.email/spec/foundations/message-format/): Every message must use the standard header and body structure, valid line endings, and legal field syntax before it enters SMTP.
- [MIME multipart structure · Email Spec](https://specification.email/spec/foundations/mime-multipart/): Use valid MIME types, boundaries, transfer encodings, and multipart nesting so every client can select a safe representation.
- [The complete email specification · Email Spec](https://specification.email/spec/): Browse sourced requirements for email format, authentication, deliverability, rendering, accessibility, privacy, security, and automation.
- [Internationalisation email requirements · Email Spec](https://specification.email/spec/internationalisation/): Unicode, language, direction, and international addresses. Browse 3 sourced, testable requirements in The Email Specification.
- [Internationalized email addresses · Email Spec](https://specification.email/spec/internationalisation/international-addresses/): Accept and preserve Unicode mailbox addresses only when every validation, storage, SMTP, and support path handles SMTPUTF8 safely.
- [Message language and text direction · Email Spec](https://specification.email/spec/internationalisation/language-direction/): Declare the message language and mark bidirectional runs so pronunciation, punctuation, numerals, and reading order remain correct.
- [UTF-8 message content · Email Spec](https://specification.email/spec/internationalisation/utf-8-content/): Encode international text consistently as UTF-8 across headers and bodies, with MIME declarations and transfer encodings that preserve every character.
- [Delivery status and bounce handling · Email Spec](https://specification.email/spec/lifecycle/bounce-handling/): Classify SMTP and delivery-status failures, stop permanent retries, back off temporary failures, and connect outcomes to the correct recipient.
- [Lifecycle email requirements · Email Spec](https://specification.email/spec/lifecycle/): Subscription, unsubscribe, complaints, retries, and expiry. Browse 3 sourced, testable requirements in The Email Specification.
- [One-click list unsubscribe · Email Spec](https://specification.email/spec/lifecycle/one-click-unsubscribe/): Bulk subscription mail needs authenticated one-click unsubscribe headers that complete without login, redirects, confirmation pages, or extra choices.
- [Retry strategy and message expiry · Email Spec](https://specification.email/spec/lifecycle/retry-expiry/): Retry transient SMTP failures with backoff, cap queue lifetime, and expire time-sensitive messages before delayed delivery becomes harmful.
- [Consent and subscription provenance · Email Spec](https://specification.email/spec/privacy/consent-provenance/): Keep verifiable evidence of how and when each recipient subscribed, what they expected, and which message purposes that choice covered.
- [Recipient data minimisation · Email Spec](https://specification.email/spec/privacy/data-minimisation/): Put only necessary personal data in message bodies, headers, links, logs, and provider metadata, with explicit retention for each copy.
- [Privacy email requirements · Email Spec](https://specification.email/spec/privacy/): Consent, tracking, data minimisation, and respectful measurement. Browse 3 sourced, testable requirements in The Email Specification.
- [Tracking pixels and remote images · Email Spec](https://specification.email/spec/privacy/tracking-pixels/): Treat open tracking as unreliable personal data collection, disclose it, minimise retention, and never make essential behavior depend on it.
- [Rendering email requirements · Email Spec](https://specification.email/spec/rendering/): HTML and CSS that survive real-world email clients. Browse 3 sourced, testable requirements in The Email Specification.
- [Inline CSS and safe fallbacks · Email Spec](https://specification.email/spec/rendering/inline-css/): Inline critical presentation, keep selectors simple, and design fallbacks for clients that remove style blocks or ignore unsupported properties.
- [Responsive email layout · Email Spec](https://specification.email/spec/rendering/responsive-layout/): Messages must fit narrow screens, preserve readable type, and keep controls usable even when media queries or viewport hints are ignored.
- [Robust email layout tables · Email Spec](https://specification.email/spec/rendering/table-layout/): Use a simple presentation-table scaffold where client support requires it, without leaking table semantics into the reading experience.
- [Dangerous active email content · Email Spec](https://specification.email/spec/security/dangerous-content/): Do not depend on scripts, forms, embedded credentials, or untrusted active content; sanitise generated HTML and provide safe web fallbacks.
- [Email header injection prevention · Email Spec](https://specification.email/spec/security/header-injection/): Treat every header value as structured data, reject line breaks from untrusted input, and let a mail library serialize addresses and fields.
- [Security email requirements · Email Spec](https://specification.email/spec/security/): Injection, dangerous content, phishing resistance, and secrets. Browse 3 sourced, testable requirements in The Email Specification.
- [Safe and trustworthy email links · Email Spec](https://specification.email/spec/security/safe-links/): Link text, visible domains, redirects, and destination context must agree, while sensitive actions require fresh server-side authorization.