SMTP
My journey to understanding what that email thing is, and why the hell someone decided to call its protocol simple.
Start from the bottom, and watch me descending into madness.
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Real-Time Blackhole List (RBL) and DNS Blocklists (DNSBL) for email antispam
How Real-Time Blackhole Lists and DNS blocklists work in email anti-spam, how mail servers query them, and where they help and where they hurt.
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The Definitive Send Email Guide
The complete guide to sending an email: parsing the recipient address, finding the receiving SMTP server, talking to it, and confirming delivery.
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DNS, rDNS, FCrDNS
Why reverse DNS alone does not prove a mail server's identity, how forward-confirmed reverse DNS (FCrDNS) works, and what that means for email delivery.
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The BCC Is a Lie
BCC is not an email header. It is a difference between the headers you write and the SMTP command you send, which is why blind copies leak so often.
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Graylisting, Nolisting, Unlisting, and Other Annoyances
Graylisting, nolisting, unlisting and other anti-spam tricks explained, with notes on why they annoy mail operators and what they actually stop.
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Mandatory Email Headers or How to Send Email (into Spam)
The mandatory headers an email needs to be accepted at all, how to compose a message by hand, and how to land in the spam folder anyway.
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How to validate an email address
Email validation is harder than a regular expression. What the RFC actually allows, what parsers accept, and how to validate an address in practice.
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SMTP components or Why sending emails is a rocket science
MUA, MSA, MTA, MDA and the rest of the SMTP chain explained, and why sending an email is more complicated than the protocol name suggests.