01
The History of Email — From ARPANET to DMARCbis
How email went from an unauthorized weekend side project in 1971 to a five-protocol authentication system in 2026 — the full 55-year history, chapter by...
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Professional Reference Guide
Every Email Leaves Evidence.
Every Email Leaves Evidence.
Learn How To Read It.
Email Infrastructure, Authentication, Header Analysis, Troubleshooting, Security, and Forensics
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Stop guessing. Start reading.
Every email sent or received contains a detailed technical record of its journey. This book provides the knowledge required to interpret these records, analyze any message, trace the sequence of servers involved, and understand the processes of authentication, encoding, filtering, and delivery.
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Authentication, demystified
SPF, DKIM, DMARC, ARC and BIMI explained the way they actually interact — not just the acronyms.
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MIME without the mystery
Multipart trees, boundaries, base64 and quoted-printable encoding, fully dissected.
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Forensic-grade reading
Trace origin, detect spoofing and reconstruct timelines straight from the header block.
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Complete header reference
Every standard header plus the sprawling world of X- and ESP-specific fields.
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Troubleshooting playbooks
Move from a user-visible symptom to a concrete root cause, fast.
5xx
SMTP codes, decoded
A complete, practical reference to the 4xx and 5xx replies and what to do about them.
Inside the book
Fifteen chapters that take you from the history of email all the way to the complete SMTP response-code reference.
02
How Email Travels — From Click to Inbox
The full SMTP delivery path, step by step — from your MUA to the recipient's mailbox, with every server and header explained along the way.
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Envelope vs Header Addresses — The Two Faces of Email Addressing
Every email carries two sender addresses, not one. Here's what envelope and header addresses do, why they differ, and why DMARC alignment depends on it.
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Email Message Structure — Headers, Body, and Everything Between
The anatomy of an email message — how the header section is built, what header folding does, and the one blank line that separates headers from body.
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All Standard Headers — Complete Reference
Every standard email header field defined — From, To, Received, Message-ID, References, and everything RFC 5322 and its companions specify — in one reference.
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Email Authentication — SPF, DKIM, DMARC, ARC, and BIMI
SPF, DKIM, DMARC, ARC, and BIMI explained as one connected system — including DMARCbis (RFC 9989–9991), now the official standard as of 2026.
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Whether you run a mail server, fight spam, or investigate abuse — Email Decoded gives you the vocabulary and the method.
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