mailv1.com
The email system, explained from the inside
Email has worked for over forty years and is used by billions of people who never
had to find out how it works. That is a compliment to the system — and the reason
almost nobody suspects how much of it was improvised.
This site explains the classic email system the way it actually operates: which
decisions from the seventies are still with us, what really goes over the wire, and
why a formally impeccable message can still end up in the spam folder.
S: 220 mail.example.com ESMTP
C: EHLO sender.example
S: 250-mail.example.com
S: 250 STARTTLS
C: MAIL FROM:<anna@sender.example>
S: 250 2.1.0 Ok
C: RCPT TO:<bert@example.com>
S: 250 2.1.5 Ok
C: DATA
S: 354 End data with <CR><LF>.<CR><LF>
This is what sending an email looks like when you listen in. Almost everything in this
exchange dates from the early eighties and is still valid, unchanged.
Why this site exists
We are building a successor to email. Doing so taught us that you only really
understand the existing system once you run it yourself — with everything that
entails: sender authorisations in the DNS, cryptographic signatures, bounces,
reputation scores handed down by recipients who owe nobody an explanation.
What we find out along the way is collected here. Not as a criticism of email — it
has proved remarkably durable — but as an honest inventory of what it takes today for
a message to arrive.
Sections
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How a by-product of the ARPANET became the most-used communication system in the world — and which decisions from back then are still with us.
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SMTP, IMAP, POP3, MIME: what actually goes over the wire, in real transcripts rather than in metaphors.
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Why a technically correct email still ends up in the spam folder, and what SPF, DKIM and DMARC change about that.
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First-hand experience of setting up and running mail infrastructure. No theory — things we broke ourselves and then repaired.
How things are written here
- Our own words. No text on this site is taken from anywhere else. Research is broad, the writing is our own.
- Primary sources first. Where an RFC exists, the RFC is in the source list — not a blog post about the RFC.
- Our own illustrations. Diagrams are drawn by us, transcripts produced by us.
- Dated. Every page carries the date it was last checked. Deliverability rules age faster than protocols.