What is DKIM?

DKIM (DomainKeys Identified Mail) adds a digital signature to outgoing emails. The receiving server uses the public key published in your DNS to verify the signature, confirming the email genuinely came from your domain and wasn't altered in transit.

The selector is a label that allows a domain to publish multiple DKIM keys. Your email provider will tell you which selector to use — common ones include google (Google Workspace), s1 / s2 (various providers), mail, and default.