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Protocols and concepts. How email authentication actually works.

3 guides in this section of the Knowledge Base. For the concepts first, start with Learn.

Every guide. In one list.

3 guides

What is ARC (Authenticated Received Chain)?How a forwarder records the authentication it saw, and when a receiver believes it.
Envelope-from vs header-from: the two sender addressesThe envelope address SPF checks and the visible From DMARC judges, side by side.
The DMARC fo tag and failure (ruf) reportsWhat fo=0, 1, d and s ask for, and why the big receivers send no failure reports anyway.

Start with one domain. See it with your own data.

Free for one domain, no card. Add one DNS record and the first reports usually arrive within a day.