DKIM (DomainKeys Identified Mail)
A cryptographic signature on your outgoing email that lets receivers verify the message wasn't altered and came from your domain.
DKIM attaches a digital signature to outgoing email using a private key, which receiving servers verify against a public key in your DNS. It proves the message is authentic and unmodified in transit.
Along with SPF and DMARC, DKIM is required by major providers for bulk senders. The three together form the authentication baseline every cold-email operation needs before volume.
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