EMAIL INFRASTRUCTURE, WITHOUT THE HAND-WAVING

Figure out how email actually works.

Notes, references, runbooks and tools for the parts of email that usually turn into a DNS lookup, a message trace, or an RFC rabbit hole.

Check a domain →Start from the beginning

317 articles · free · vendor neutral · open source

START WITH THE PROBLEM

What are you trying to do?

Something is brokenStart with the symptom: bounced, delayed, spam, authentication or TLS.Check a domainInspect public MX, SPF, DKIM, DMARC, MTA-STS and TLS-RPT configuration.Learn email end to endFollow DNS → SMTP → authentication → TLS → deliverability → security.Find the standardMap the protocol you are working with back to its RFCs and registries.

THE LIBRARY

Use the level of detail you need.

Learn42 guides

Concepts and architecture. Start here when you need the mental model before the syntax.

→Reference151 references

Protocols, DNS records, headers, status codes, standards and exact terminology.

→Do124 procedures

Runbooks for testing, deploying, migrating, monitoring and troubleshooting email.

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Glossary →Browse topics →Search everything →Tools →

Why this exists. Email is old, distributed and full of implementation details that get flattened into bad advice. howto.email keeps the protocol details close to the practical work: see the record, understand what it means, read the standard, make the change, and test again. About the project →