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DomainKeys Identified Mail (DKIM)
DomainKeys Identified Mail (DKIM)
DomainKeys Identified Mail (DKIM) verifies an email’s domain and ensures it has not been tampered with in transit. The receiving email service can then filter or reject email that fails the DKIM check. In order for DKIM to verify an emails domain it uses public key encryption to check email by creating a hash using the content of each outbound email. The sending service then encrypts the hash with its private key and adds it to the email header. This is the DKIM signature.
The receiving email service looks up the public key in the sender’s DKIM DNS (DOMAIN NAME SYSTEM) record then uses the public key to decrypt the DKIM signature on the email. It also generates a hash of the email in the same way the sending email service did. If the hash matches the decrypted DKIM signature then the email passes the DKIM check. This means the email came from where it says it came from and has not changed in transit.
Using DomainKeys Identified Mail (DKIM) in your organisation - GOV.UK.pdf