What Is DKIM and How Does It Work?
By Emil Kristensen CMO
@ Sleeknote

Email has been one of the most common and essential modes of communication in both personal and business settings for a long time. However, with the widespread use of email, spam messages and email frauds have also become a significant threat. Authentication mechanisms such as DomainKeys Identified Mail (DKIM) have become essential to ensure email security, privacy, and authenticity. In this article, we will explore DKIM technology, its importance, history, technicalities, implementation, challenges, advantages, and future trends in email authentication.

The Importance of Email Authentication

According to a report, the cumulative global cost of email fraud and fake emails is predicted to reach $319.6 billion by 2022. These statistics signify the severity of email fraud and emphasize the importance of email authentication technologies such as DKIM. Email authentication is a technique that helps safeguard the integrity and authenticity of email messages. By using DKIM, email authentication becomes more secure as it provides a digital signature to the email message in transit, which can be validated by the recipient’s email server. By validating the email signature, the recipient’s email server can detect malicious or spoofed emails instantly and avoid related problems such as phishing, scams, and spam.

The History and Evolution of DKIM

The inception of DKIM dates back to 2004 when engineers from Yahoo!, Cisco, and PGP Corporation united to develop an email authentication system that could verify emails’ integrity and authenticity. The idea behind DKIM was to counteract email spoofing by adding cryptographic techniques to the process of authenticating email messages. DKIM absorbed the best features of its predecessors such as DomainKeys and Identified Internet Mail and became a de facto email authentication standard. The Internet Engineering Task Force (IETF) has standardized DKIM under RFC-6376, and its usage has become ubiquitous among most email service providers, email clients, and organizations.

How DKIM Works – A Technical Overview

DKIM works by signing the email message header and content with a unique cryptographic key generated by the email sender’s domain. When the email message is delivered to the recipient’s email server, the server extracts the domain’s public key from the DNS record and verifies the signature’s authenticity. If the signature is valid, the email message is classified as legitimate and does not get marked as spam by the recipient’s email client. The technical process of DKIM is complicated, involving various concepts such as hashing, public and private keys, digital signatures, DNS lookups, and many others.

The Role of Public and Private Keys in DKIM

DKIM operates via a public key cryptography mechanism, which involves using a pair of keys – a public key and a private key. The private key is used to sign the email message while the public key is used to verify the signature. Ideally, the private key is kept secret by the sender, while the public key is published in the DNS record of the domain. In this way, the email message can be verified via the public key stored in the DNS without compromising the private key.

Implementing DKIM on Your Email Server

Implementing DKIM for your email servers requires specific technical knowledge and skills as it involves various procedures such as generating public-private key pairs, configuring your DNS record, modifying the email message headers, testing and monitoring. There are several manuals, guides, and tutorials online that can help you get started. Additionally, various online services can help you implement DKIM for your domain, which may require one-time or subscription-based payments.

Common Challenges with DKIM Implementation and How to Overcome Them

DKIM implementation can face several challenges. One common challenge is with the format of email messages. If the email message gets modified during transit by intermediate email servers, the DKIM signature validation can fail, leading to emails being marked as spam by the recipient’s email client. Another challenge is with DNS records, which are critical to DKIM implementation. A mistake in the DNS record can lead to DKIM signature validation failing or invalid. Overcoming these and other challenges requires a thorough understanding of the technical intricacies of DKIM. It is vital to test and monitor your DKIM implementation regularly to avoid any problems.

DKIM vs SPF vs DMARC – Understanding the Differences

DKIM, Sender Policy Framework (SPF), and Domain-based Message Authentication, Reporting & Conformance (DMARC) are all email authentication mechanisms used to safeguard emails. However, they differ in their approach and functionality. DKIM signs the message content, while SPF validates the source IP address’s identity, DMARC combines both DKIM and SPF, and also provides a mechanism to instruct receiving email servers to act upon validation results, such as rejecting, marking, or quarantine email messages. While these technologies are not mutually exclusive, their combined use can provide a comprehensive email authentication framework for organizations.

Advantages of Using DKIM for Your Business Emails

There are several advantages to using DKIM for your business emails. By implementing DKIM, you can safeguard the authenticity and integrity of your email messages, which can improve your email deliverability rate and avoid spam folders. DKIM can also protect your organization’s reputation from email spoofing and phishing attacks, which can cause significant financial and reputational damage to your organization. Additionally, DKIM can provide your customers and clients with a higher degree of trust in your email communications, which can translate to increased engagement and conversions.

Future Developments and Trends in Email Authentication

The future of email authentication is expanding. Various new technologies and mechanisms such as Brand Indicators for Message Identification (BIMI), Certificate Authority Authorization (CAA), and others are being developed to improve email authentication, privacy, and security. These technologies aim to standardize email authentication, reduce email fraud, and provide a better email user experience. It is essential to keep up with these developments to ensure your email communication remains secure and reliable.


In conclusion, DKIM is an essential email authentication mechanism that helps safeguard the authenticity, integrity, and privacy of email messages. DKIM has a long history of development, evolution, and standardization. Implementing DKIM on your email servers requires specific skills and technical knowledge, and overcoming implementation challenges is crucial to ensure successful email authentication. DKIM is not the only technology to secure emails, and other mechanisms such as SPF and DMARC provide additional layers of protection. Incorporating these technologies into your email authentication framework can provide a comprehensive and robust email communication environment for your organization. As email communication evolves, keeping up with developments and trends in email authentication is critical to ensure secure, reliable, and trusted email communication.