What Is DKIM? A Breakdown Of The Signature
That Secures Your Messages

In today’s digital environment, characterized by widespread phishing, spoofing, and identity theft, it is imperative for organizations to leverage all available resources to safeguard their email communications. Among the most vital and effective measures in this ongoing fight is DKIM (DomainKeys Identified Mail), a robust protocol that employs cryptographic signatures to authenticate the validity of email messages.

Grasping the mechanics of DKIM and its role within the larger email authentication ecosystem is essential for businesses, IT professionals, and domain administrators. This guide aims to elucidate the fundamental purpose of DKIM, its key components, and how its signature contributes to ensuring both message integrity and sender verification.


What Is DKIM?


DKIM, or DomainKeys Identified Mail, serves as a method for authenticating emails to identify and prevent spoofed sender addresses. It enables recipients to validate both the origin and the integrity of an email message.

This process involves appending a digital signature to the header of the email, which the recipient's server can authenticate by accessing a public key from the sender’s DNS records. This system ensures two essential confirmations:

  • The email really came from the claimed domain (authentication)

  • The message content has not been altered (integrity)


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How DKIM Works to Authenticate Email Messages


DKIM Uses Public-Key Cryptography

DKIM operates by creating a distinctive digital signature through the use of a private encryption key. This signature is included with every email sent. Upon receipt of the message, the recipient's server accesses the sender's public key from the DNS to confirm the message's integrity. If the signature, once decrypted, corresponds with the contents of the email, the message successfully meets DKIM authentication standards.


Email Headers and Body Are Signed

DKIM (DomainKeys Identified Mail) authenticates specific components of an email, typically including the "From," "To," "Subject," and "Date" headers, along with the email body. These components are hashed and subsequently encrypted using the sender's private key. This process guarantees that any modification made during transmission, no matter how minor, will render the signature invalid and result in a failed verification. You can find more details by visiting this source.


Components of a DKIM-Signed Email


DKIM-Signature Header Field

The implementation of DKIM results in the inclusion of an additional header known as DKIM-Signature within the email. This header encompasses various pieces of metadata, such as the domain (d=), selector (s=), algorithm (a=), and the digital signature (b=). The receiving server utilizes this header to verify the legitimacy of the message.



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DNS TXT Record With Public Key

In order to verify DKIM signatures, recipients must obtain the public key of the sender. This key is maintained in a specifically structured DNS TXT record associated with a subdomain, such as selector._domainkey.example.com. The selector serves to distinguish the appropriate public key to utilize when a domain has multiple DKIM records in place.


Benefits of Using DKIM for Email Security


  • Protects Against Email Spoofing and Phishing: DKIM verifies the authenticity of messages sent from your domain, significantly complicating efforts by malicious actors to spoof your identity. This fosters confidence among Internet Service Providers (ISPs) and recipients, thereby decreasing the chances of your emails being flagged as spam or exploited for phishing schemes.

  • Preserves Message Integrity: DKIM authenticates both the message headers and body, ensuring that even the alteration of a single character during transmission will lead to a failure in the DKIM verification process. This mechanism ensures that the content received by your recipient is precisely what was originally dispatched.


Setting Up DKIM on Your Domain


  • Generate a Key Pair: A majority of email service providers, including Google Workspace, Microsoft 365, and Zoho, provide integrated features for the creation of DKIM private and public keys. The private key is securely stored on the server that sends the emails, whereas the public key is made available through DNS records.

  • Publish the Public Key in DNS: To set up your public key, you must establish a TXT record that incorporates a selector for identification purposes. This record is generally formatted as selector._domainkey.yourdomain.com. The value should start with v=DKIM1; k=rsa; p=, followed by the actual public key itself.

  • Enable DKIM Signing on Your Mail Server: After you have successfully positioned your keys, it is essential to set up your mail server or Email Service Provider (ESP) to authenticate outgoing messages with the private key. The majority of service providers offer an option to enable this feature through their administrative interface.