DKIM selector
A DKIM selector is a short label included in a message's DKIM-Signature header that tells a receiving server exactly which DNS TXT record holds the public key needed to verify it, at the hostname selector._domainkey.example.com. Selectors let one domain publish multiple DKIM keys at once -- a common setup when several outbound mail systems (a marketing platform, a helpdesk tool, an internal mail server) each sign with their own key and selector, such as mandrill._domainkey.example.com or google._domainkey.example.com. A verification failure often traces back to a selector mismatch rather than a bad signature: the sending system changed selectors, rotated a key, or the DNS record for that specific selector was never published or was deleted during cleanup.
By AdminKit team, Netbase JSC · Updated