Email Specifications

Construct structurally valid email messages adhering to RFC 5322 grammar, strict CRLF line endings, 998-character line limits, and standard header folding rules.

Emit mandatory RFC 5322 header fields (From, Date, Message-ID), structured recipient fields, and machine-readable metadata while preventing header duplication.

Structure rich email payloads using standardized MIME multipart trees (alternative, related, mixed), paired plain-text fallbacks, and collision-resistant boundary delimiters.

Publish a single, bounded SPF policy that authorizes legitimate envelope senders without exceeding the 10-DNS-lookup limit or using overly permissive qualifiers.

Cryptographically sign outgoing email messages with DKIM using aligned domains, minimum 2048-bit keys, canonicalization, and regular selector rotation.

Enforce domain-aligned email authentication with a DMARC policy that instructs receivers how to handle unauthenticated mail and generates aggregate feedback reports.

Configure Forward-Confirmed Reverse DNS (FCrDNS) on every sending IP address, ensuring the PTR record matches the forward A/AAAA record and the SMTP EHLO greeting.

Maintain pristine sender reputation through automated bounce management, double opt-in confirmation, inactive subscriber sunsetting, and spam trap avoidance.

Process user spam complaints in real-time through ISP Feedback Loops (FBL) and RFC 5965 Abuse Reporting Format (ARF) to maintain spam complaint rates below 0.10%.

Structure email markup with true semantic HTML elements (h1-h3, p, ul, ol), document language declarations, and clear hierarchical reading order.

Meet WCAG 2.2 AA contrast standards (minimum 4.5:1) while architecting email designs for dark mode color inversions across Outlook, Apple Mail, and Gmail.

Provide meaningful alternative text for informative images, null alt attributes for decorative graphics, and styled fallbacks when remote images are blocked.

Construct bulletproof HTML email scaffolds using presentation tables, role="presentation" ARIA semantics, 600px max-width containers, and Microsoft Outlook ghost tables.

Inline critical CSS rules directly onto HTML elements to survive webmail style-stripping while leveraging embedded style blocks for media queries and dark mode.

Design responsive email templates using fluid-hybrid layouts, mobile-first breakpoints, single-column column stacking, and 44x44px touch targets.

Understand remote tracking pixel mechanics, Apple Mail Privacy Protection (MPP) proxy caching, GDPR/ePrivacy compliance, and pseudonymized analytics.

Maintain immutable cryptographic records of subscriber consent, capturing timestamps, IP addresses, signup URLs, form identifiers, and policy versions for regulatory compliance.

Minimize Personally Identifiable Information (PII) transmitted across email bodies and URL parameters, enforcing masking, TLS transport, and ephemeral log retention.

Standardize on end-to-end UTF-8 encoding across email headers and MIME bodies using Quoted-Printable or Base64 transfer encodings to prevent character corruption.

Architect bidirectional and Right-to-Left (RTL) email layouts with document-level dir="rtl" declarations, mirrored table alignments, and isolated BiDi spans.

Support Internationalized Domain Names (IDN) via Punycode and handle non-ASCII local-parts using RFC 6530 Email Address Internationalization (EAI) and SMTPUTF8.

Implement RFC 8058 one-click list unsubscribe headers with HTTP POST endpoints, mailto fallbacks, DKIM signature protection, and zero login barriers.

Classify and process hard and soft delivery failures using RFC 3463 enhanced status codes, Variable Envelope Return Path (VERP), and instant suppression automation.

Configure outbound SMTP queue management with exponential backoff, randomized jitter, greylisting survival delays, and strict 72-to-120-hour queue retention limits.

Prevent SMTP and RFC 5322 header injection vulnerabilities by neutralizing CRLF control characters and using typed mail serialization libraries.

Enforce HTTPS-only hyperlinks, eliminate phishing link text mismatches, and protect email click-tracking redirects against open redirect vulnerabilities using HMAC signatures.

Eliminate prohibited active content (JavaScript, iframes, embedded objects, raw forms) and restrict high-risk file attachment extensions to prevent malware classification.

Embed structured Schema.org JSON-LD markup in transactional emails to render interactive One-Click Actions, order summaries, and flight/event cards in Gmail and Apple Mail.

Publish standards-compliant calendar meeting invites, updates, and cancellations using iCalendar (RFC 5545) and iMIP (RFC 6047) multipart attachments.

Attach documents and assets using RFC 2183 Content-Disposition, RFC 2231 international filename encoding, Base64 transfer encoding, and 10MB size ceilings.