Authentication
What is DomainKeys Identified Mail (DKIM)?
An authentication method that cryptographically signs outgoing email so recipients can verify it was not altered and came from the claimed domain.
DKIM adds a digital signature to message headers using a private key held by the sender, while the matching public key is published in a DNS TXT record at a selector subdomain. Receiving servers fetch the public key and verify the signature, confirming the signed headers and body were not tampered with in transit. Unlike SPF, DKIM survives most forwarding because the signature travels with the message.
Why it matters for cold email
A valid DKIM signature is a baseline trust signal for cold outreach and the more reliable of the two paths to DMARC alignment. Using a unique signing key per sending domain and rotating keys periodically helps protect your sender reputation across mailbox providers.
Related terms
Stop guessing at deliverability.
Scheduler Zero handles authentication, warmup, and sender reputation so your cold email lands in the inbox, not the spam folder.