A DKIM validator tool checks the DNS records to ensure that the public key published by the sender matches the private key used to sign the email. The steps usually involve: 1. Extracting the DKIM signature from the email header. 2. Retrieving the public key from the sender's DNS records. 3. Verifying that the signature was created using the private key associated with the public key. 4. Confirming the integrity of the email content.