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What Is DKIM? What is a DKIM Signature?

DKIM is an email authentication process that allows a receiving server to check the signer’s domain name against their public key. If it matches, the message is authenticated and the receiver believes that the sender is who they say they are and can be trusted with content. The DKIM signature will also identify what type of encryption was used in order for mail servers to know how to decrypt messages. 

Definition of DKIM

DKIM allows an organization to take responsibility for transmitting a message by signing it in a way that mailbox providers can verify. The protocol is made possible through cryptographic authentication, and organizations should use the tone of voice that's most professional when they sign their authentic messages with DKIM.

Implementing email authentication technology like DKIM is one of the best ways to protect your employees and customers from targeted email attacks. Earlier this month, we published a post breaking down what SPF (Sender Policy Framework) is and why it matters. This week, we turn to another email authentication protocol: DomainKeys Identified Mail or DKIM for short.

How Does DKIM Work?

There are three main steps to the DKIM signing process. First, the sender identifies what fields they want to include in their DKIM record signature. These fields include the “from” address, the body, the subject, and many others. These fields must remain unchanged in transit, or DKIM authentication will fail.

Once the hash string is generated, it's encrypted with a private key that only the sender has access to. The DKIM signature remains intact throughout various email providers and after sending an email, but can be validated by using public keys and decrypting back into its original form.

When the receiver generates its own hash of the fields included in a DKIM signature, it compares them with just decrypted strings. If they match, we know two things: One, that changes to the contents were not made during transit and Two, this email was signed by someone who truly owns it!

What is a DKIM Signature?

Think about it this way- if the sender of a message is able to change parts of their email after it has been sent, that means they can also lie and pretend someone else wrote them. But with DKIM signatures being hashes created from components within the messages themselves, there's no chance for sneaky tricks like these!

To create the signature, the sender uses a private key to encrypt their message and produce an encrypted hash. The recipient email server then does this as well with the public key of the sender's domain. If both hashes are identical after decrypting them using each other’s keys, DKIM validation passes for that message.

DKIM signatures, with encryption, make sure that recipients don't fall victim to phishing and malware attacks from intercepted messages.

Conclusion

DKIM signatures are a way to verify that an email message is from the organization it claims to be coming from. If you want your emails to have this protection, contact us and we can help secure your domain with DKIM so that your customers will recognize your messages as legitimate.