What is DomainKeys Identified Mail (DKIM)?

DomainKeys Identified Mail (DKIM) is an email authentication method. Using public key cryptography, the protocol allows email senders to take responsibility for their messages. DKIM enhances the trustworthiness of email by verifying that the email’s content remains unaltered, from when it leaves the initial sending server until it reaches the recipient.



A Brief History of DKIM

DKIM was set up in response to the escalating issue of email-based threats and abuses, such as spam and phishing attacks. It was created by merging two similar technologies: Yahoo!’s DomainKeys and Cisco’s Identified Internet Mail.


The merger aimed to create a unified standard that would gain widespread acceptance and efficacy. Finalized as RFC 4871 in 2007 and later updated to RFC 6376, DKIM offered a robust framework for email authentication that could be universally implemented.



How does DKIM work?

The DKIM process works as follows:


  • Signing the email:

    When an email is sent, the DKIM system generates a signature based on the content of the email and the sender’s private key. This signature is then attached to the email’s header as it leaves the sending server.

  • Verification upon receipt

    The receiving server extracts the DKIM signature and retrieves the sender’s public key from the DNS. It then uses this public key to verify the signature against the email’s content.


  • Authentication and action

    A successful authentication verifies that the email was indeed sent from the domain it claims to be from. It also confirms that its content is authentic and unaltered. The receiving server uses this information to make informed decisions about the email’s delivery, such as bypassing spam filters or flagging potential forgeries.

What is DKIM’s Role in Email Security?

DKIM significantly contributes to the safety of email communication. It helps prevent fraud, email spoofing, and other email-based cyber threats. It’s also key to broader email authentication strategies, such as Sender Policy Framework (SPF), and Domain-based Message Authentication, Reporting, and Conformance (DMARC). 

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