What a good
email does.
A sourced specification for every technical detail that matters: from From:and MIME to DMARC, one-click unsubscribe, accessible HTML, and dark mode. Written for humans and agents.
The message
The delivery
The experience
The relationship
One email. All of these responsibilities.
Email evolves.
So does the spec.
Full changelog →Every detail.
A reason behind it.
Ten areas, grounded in email standards.
Pick the part of your email you’re working on.
- 3 topics↗
Foundations
Message format, headers, MIME, identity, and the envelope.
- 7 topics↗
Authentication
SPF, DKIM, DMARC, transport security, and domain trust.
- 3 topics↗
Deliverability
Reputation, list quality, bounces, and inbox placement.
- 3 topics↗
Accessibility
Readable, operable messages for people of all abilities.
- 3 topics↗
Rendering
HTML and CSS that survive real-world email clients.
- 3 topics↗
Privacy
Consent, tracking, data minimisation, and respectful measurement.
- 3 topics↗
Internationalisation
Unicode, language, direction, and international addresses.
- 3 topics↗
Lifecycle
Subscription, unsubscribe, complaints, retries, and expiry.
- 3 topics↗
Security
Injection, dangerous content, phishing resistance, and secrets.
- 3 topics↗
Automation
Machine-readable actions, calendars, receipts, and agent use.
Read it.
Check it.
Make it better.
Open the checklist →Every topic explains what it is, why it matters, and how to implement it. Every item in the checklist is a yes/no.
- Required23
- Leaving it out breaks delivery, authentication, or access for some recipients.
- Recommended9
- What modern mailbox providers, clients, and recipients expect.
- Optional1
- Useful when the context calls for it.
- Avoid1
- Outdated, harmful, or unsafe.
Audit a delivered message. Fix what’s missing, send a test, then re-check.
Same spec.
Another pair of eyes.
Let your agent query the same specification through a read-only MCP server. Search topics, fetch guidance, build checklists, or ask what changed.
Standards, not folklore. Primary sources on every topic.
Provider agnostic. Use any ESP, MTA, or template system.
Test the delivered message. Verify what actually arrives.