Email Decoded

Every email you've ever sent left a paper trail. Can you read it?

Open any email's raw source and you'll see a wall of headers most people never look at twice - Received: chains, DKIM-Signature:, Authentication-Results:, X- fields nobody ever explained to you. That wall of text is a complete, timestamped record of exactly how the message traveled, who touched it, and whether it's telling the truth about who sent it.

Email Decoded teaches you to read it, line by line, until a raw source view stops looking like noise and starts looking like a story.

Whether you're a systems administrator debugging why legitimate mail is landing in spam, a security engineer investigating a business email compromise, or a developer integrating an ESP - this is the reference built for the moment you need the real answer, not a forum thread from 2014.

What's Inside

15 chapters • 8 original diagrams • every RFC citation checked against the primary source
• SMTP delivery, message structure, and the full header reference
• SPF, DKIM, DMARC, ARC, and BIMI authentication, explained mechanism by mechanism
• MIME, encoding, and Content-Type - how email actually carries attachments and rich content
• TLS, MTA-STS, DANE, S/MIME, and PGP encryption
• Inbound gateways, spam scoring, and the complete SMTP response code reference
• Email forensics - reconstructing a message's true path from its headers
• A Quick Reference appendix, full Glossary, and troubleshooting decision flowchart

Built Differently

Every RFC citation is verified against the primary source, not paraphrased from a blog post paraphrasing another blog post. It's current through 2026, including RFC 9989/9990/9991 (DMARCbis) and the Google/Yahoo/Microsoft bulk-sender enforcement rules. And it doesn't stop at theory - every mechanism is paired with a real header example, a real Postfix config block, or a worked diagnostic case.

Who It's For

Systems and email administrators, deliverability and security engineers, incident responders, and developers of email infrastructure. Foundational knowledge of DNS and the command line is assumed - no prior email-internals expertise is.

Written by Iovo - a pen name for an IT professional with 25+ years designing, implementing, and supporting enterprise email security and SMTP boundary systems, with a focus on SPF, DKIM, and DMARC.

Every email leaves evidence. Learn how to read it.