Health Library
How email authentication actually works
Three guides and the articles that sit under them. Every one is written from the standards, cites the section it came from, and ends with the test that proves it on your own domain.
Guide
DMARC, from a first record to enforcement
The only record that governs the address your recipient actually sees. What it does, what it does not, and how to reach enforcement without breaking your own mail.
A DMARC checker that is actually free
No account, no trial, no report held back behind an email address. Here is what it checks and what makes a DMARC check wrong.
How to set up DMARC
From no record to enforcement, in five steps. The first takes ten minutes; the rest are mostly waiting and reading.
p=none, quarantine or reject?
Three policies, one of which protects nothing. What each does to your mail and how to move between them without breaking anything.
What is DMARC?
The only email record that looks at the address your recipient actually sees, and the only one that stops somebody sending in your name.
Guide
Email authentication, explained by what each part proves
Three records, three different jobs, and only one of them stops somebody sending mail in your name. Here is what each proves and the order to fix them in.
SPF: too many DNS lookups
Ten is the limit, the lookups inside your includes count against it, and past ten SPF fails for every message you send. Here is how to get back under.
What is DKIM?
A cryptographic signature on every message you send, and the only identifier that survives being forwarded.
What is SPF?
A published list of the servers allowed to send for your domain, and the ten-lookup limit that quietly breaks a lot of them.
Guide
Why your mail lands in spam, in the order worth checking
Deliverability problems have a small number of causes and a reliable order to work through them. Authentication first, because it is the only part you can prove.
The bulk sender requirements, and which parts bite
Three receivers, one shared list of requirements, and rejections rather than filtering when you miss them. Here is what each one asks for.
Looking for an MXToolbox alternative
What this does differently, what it does not do at all, and an honest note on when the other one is the right tool.
Why are my emails going to spam?
Six causes, in the order worth checking. The first two you can prove in about a minute; the rest take longer and matter less often.
Glossary
Definitions
One page per term, for when you want the meaning rather than the guide.
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.