What is the difference between DKIM and DomainKey and how do you implement DomainKey?
Michael Ko
Co-founder & CEO, Suped
Published 3 May 2025
Updated 19 Aug 2025
5 min read
When delving into email authentication, it's easy to encounter terms that seem similar but have distinct histories and purposes. Two such terms are DomainKeys and DomainKeys Identified Mail (DKIM). While they share a common lineage, understanding their differences is crucial for anyone managing email infrastructure or aiming for optimal deliverability.
Many years ago, email authentication was a Wild West. Spam and phishing were rampant, and recipients struggled to verify the legitimacy of incoming messages. Initiatives like Sender Policy Framework (SPF) emerged to help, but there was a need for cryptographic assurance that an email’s content hadn't been tampered with and truly originated from the claimed domain.
This is where DomainKeys first came into play, an early attempt to provide this assurance. However, as the email landscape evolved, so did the need for more robust and flexible authentication methods, leading to the development and widespread adoption of DKIM, which effectively superseded its predecessor.
DomainKeys, developed by Yahoo!, was an early email authentication system designed to verify the sender of an email and ensure that the message had not been altered in transit. It used a cryptographic signature added to the email header, which was then verified against a public key published in the sender's DNS records.
While innovative for its time, DomainKeys had limitations. It only supported one signature algorithm and had a specific header field, DomainKey-Signature. It laid the groundwork, but a more comprehensive solution was needed to handle the complexities of modern email sending.
This is where DomainKeys Identified Mail (DKIM) comes in. DKIM emerged from the collaboration between the developers of DomainKeys and another proposal called Identified Internet Mail. This combined effort resulted in a more robust and flexible standard, specified in RFC 4871, which became the widely accepted successor.
Key differences between DomainKeys and DKIM
While conceptually similar, the practical and technical differences between DomainKeys and DKIM are significant. DKIM was designed to be more versatile and address some of the shortcomings of its predecessor. It allows for multiple signature algorithms and provides more options for validating both header and body content, enhancing its security capabilities.
The signature field itself is also different. DomainKeys uses DomainKey-Signature, whereas DKIM uses DKIM-Signature. This seemingly small change indicates a fundamental shift in the protocol's architecture. Most importantly, DKIM became the standard that email service providers and major mailbox providers adopted, while DomainKeys faded into obscurity.
DomainKeys
Origin: Developed by Yahoo!
Status: Largely deprecated and unsupported.
Signature header: DomainKey-Signature
Algorithms: Limited to specific cryptographic algorithms.
DKIM (DomainKeys Identified Mail)
Origin: Standardized by the IETF, merging DomainKeys and Identified Internet Mail.
Status: Widely adopted and current industry standard.
Signature header: DKIM-Signature
Algorithms: Supports multiple cryptographic algorithms for flexibility.
For a deeper dive into how DKIM functions alongside other crucial email authentication methods like SPF and DMARC, you can explore articles on how SPF, DKIM, and DMARC work.
Implementing DomainKey: why it's not recommended
Given that DomainKeys is largely deprecated and DKIM has become the standard, attempting to implement DomainKey today is generally not recommended. Most modern email servers and authentication systems no longer check for DomainKey signatures, making any effort to implement it largely pointless.
Why DomainKeys implementation is not advised
Lack of support: Email service providers and mailbox operators focus on DKIM, not DomainKeys.
Performance overhead: Signing emails with an unsupported protocol consumes server resources without benefit.
Maintainability: You'll struggle to find current documentation, libraries, or support.
No deliverability benefit: It won't improve your inbox placement or protect against spoofing.
Instead of focusing on DomainKeys, I strongly advise concentrating your efforts on properly implementing DKIM. DKIM, along with SPF and DMARC, forms the trifecta of modern email authentication, essential for protecting your domain from phishing and spoofing and ensuring your emails reach the inbox. You can learn more about configuring DKIM in our guide on how to configure DomainKeys DKIM for email authentication.
Here's an example of what a DKIM record (a TXT record in your DNS) typically looks like. Note the v=DKIM1 tag, indicating it's a DKIM record, unlike the older DomainKeys format.
Example DKIM DNS TXT recordDNS
default._domainkey.yourdomain.com IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDl3d+M7V1yN6F7E8t4H8wz9sX2j5yL5q0r7tQ0iQ2R5k0zJ3x7yP1c0lq8L7r4v1c1t0c1r2w0x3y4z5a6b7c8d9e0f="
Views from the trenches
Best practices
Always prioritize implementing DKIM over DomainKeys for modern email authentication.
Ensure your DKIM DNS records are correctly published and validated.
Integrate DKIM with SPF and DMARC for comprehensive email security and brand protection.
Regularly monitor your email authentication status to catch any misconfigurations quickly.
Common pitfalls
Attempting to implement DomainKeys, as it is obsolete and will not improve deliverability.
Using outdated email sending systems that still rely on deprecated protocols.
Overlooking the performance implications of unnecessary cryptographic signing.
Failing to update or rotate your DKIM keys, which can lead to authentication failures.
Expert tips
I recommend checking your mail transfer agent (MTA) or email service provider settings.
Focus on the current standards for email authentication for optimal results.
While older systems might still have remnants, they aren't worth the effort to configure.
Always aim for the latest secure configurations for the best email deliverability.
Expert view
Expert from Email Geeks says DomainKeys have been deprecated by DKIM, making them largely irrelevant for current email authentication practices.
2021-10-21 - Email Geeks
Expert view
Expert from Email Geeks says most email recipients are no longer checking for DomainKeys, rendering its implementation pointless. The fundamental signing process is similar to DKIM, but providers typically don't support it anymore.
2021-10-21 - Email Geeks
Moving forward with modern email authentication
In the world of email authentication, DomainKeys was a foundational step, but DomainKeys Identified Mail (DKIM) is the robust and universally adopted standard. While the question of implementing DomainKey might arise from a historical or learning perspective, the practical reality is that all efforts should be directed towards configuring and maintaining DKIM.
Proper DKIM implementation is critical for your email deliverability and to safeguard your domain's reputation. It assures receiving servers that your emails are legitimate and haven't been tampered with, reducing the likelihood of them landing in spam folders or being blocklisted (or blacklisted). You can also use tools available to generate DKIM keys.
By focusing on modern standards like DKIM, along with SPF and DMARC, you ensure your email sending infrastructure is secure, trusted, and efficient, maximizing your chances of successful inbox placement. Remember to stay updated with email authentication best practices to adapt to the evolving email security landscape.
Developed by Yahoo!
