DMARC vs SPF vs DKIM: The Complete Guide

Email authentication relies on three core protocols: SPF authorizes the server, DKIM verifies the payload, and DMARC enforces the policy. Google and Yahoo require authentication from bulk senders, and together these three are how a receiver decides whether mail claiming to be from you really is.

How the three fit together

SPF: the guest list

SPF is like a guest list for your domain. It is a DNS record that lists all the IP addresses and servers authorized to send email on behalf of your domain.

Standard SPF only checks the “Return-Path”. Without DMARC alignment, the “Header From” stays vulnerable to spoofing.

SPF is capped at ten DNS lookups. On Business and above, SentraDMARC keeps you under that cap by flattening the includes behind a single one. Fixing SPF PermError covers what happens past the cap.

DKIM: the digital seal

DKIM adds a digital signature to your emails. The signature lets a receiver verify that the content was not tampered with in transit.

Unlike SPF, DKIM survives email forwarding. That makes it the most resilient form of authentication for complex mail flows.

DMARC: the enforcer

DMARC ties SPF and DKIM together. It tells receiving servers how to handle failures, with a none, quarantine or reject policy.

It is the only one of the three that tells you who is sending email as you.

SentraDMARC shows you when each step towards p=reject is safe: monitor, then quarantine and reject at rising percentages. Each step is one approval of yours.

It never moves your policy for you, on a schedule or otherwise.

How hosted SPF stays correct

With SentraDMARC hosting your SPF record (Business and above), it also stays correct.

When a provider changes their own ranges, your SPF is re-flattened automatically instead of silently breaking.