Email authentication is the set of DNS records that let a receiving server check an email really comes from the domain it claims. There are three, and they work together.
- SPF lists the servers allowed to send for the domain.
- DKIM signs each email so it can't be changed or faked on the way.
- DMARC ties them to the From address and says what to do when they fail.
What Gmail and Yahoo require
Since February 2024, everyone sending to Gmail or Yahoo needs SPF or DKIM. Bulk senders (Google's line is around 5,000 emails a day to Gmail) need all three, with DMARC aligned, plus one-click unsubscribe for marketing mail. Missing records mean more spam-folder placement or outright rejection.
For cold email
Every sending domain needs all three before its first campaign, plus an MX record so replies arrive. mailzy checks SPF, DKIM, DMARC and MX on every connected domain, and the free domain health checker checks any domain in one go.