DKIM
DKIM (DomainKeys Identified Mail) is an email authentication method where the sending server adds a cryptographic signature to each message, which receivers verify using a public key published in the domain's DNS.
Also called: DKIM, DomainKeys Identified Mail
Why it matters
DKIM lets a receiving server confirm that a message was authorized by the signing domain and that signed parts were not changed in transit. The sender keeps a private key and publishes the matching public key as a DNS TXT record at a selector, such as selector._domainkey.example.com. The signature travels in a DKIM-Signature header.
For cold email, DKIM is one of the basic records mailbox providers expect before trusting a sender. It works alongside SPF, which lists the servers allowed to send for a domain, and DMARC, which tells receivers what to do when checks fail. Each sending platform a team uses, such as a CRM or sequencer, usually needs its own DKIM setup.
Example
A startup sets up a new domain for outbound email in its email provider. In the admin console it generates a DKIM key, then adds the TXT record the provider gives it to its DNS under the selector name shown. After DKIM signing is turned on, the headers of its outgoing emails show DKIM as passing for its domain.
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