SPF, DKIM and DMARC are three small DNS records that decide whether your mail is trusted, quietly filtered, or refused outright. The specs that define them are precise and almost unreadable; the vendor guides that explain them are usually a setup wizard with the reasoning removed. These pages sit in between — what each record is, where it actually lives, what breaks it, and how to tell which of those is happening to you.
Everything here is written from the checks our own free tools run, so the specifics — which selectors we probe, which limits we enforce, what counts as a failure — match what you get back when you run one.
SPF, DKIM and DMARC — what each record proves, where it lives, and which one is failing when mail gets refused.
Why mail that authenticates correctly still lands in spam: blacklists, sender reputation, SMTP refusals, warmup.
The addresses that should never have entered your list, and the signups that were never a person.
What the message itself does to your delivery odds — subject lines and spam triggers.