What Is DKIM: A Guide for Email Marketers

What is DKIM
Josh M
Author: J. Michaels
Mateo B
Reviewed by: Mateo Beltroy
What is DKIM

Did you know that nearly 85% of all email traffic is spam? That’s a staggering number, and it’s why you should be aware of DKIM, otherwise known as DomainKeys Identified Mail.

This email authentication method is designed to help protect you and your business from email spoofing and phishing attacks.

Yet, how does it really work, and why is it so critical for email marketing?

What is DKIM?

DKIM, or DomainKeys Identified Mail, is an essential email security standard that you should understand, as it helps identify if messages have been tampered with while in transit between sending and receiving servers. The DKIM configuration process involves adding a DKIM record to your DNS.

Implementing DKIM offers a wide range of benefits. For example, it improves (or maintains) your domain’s reputation by ensuring your emails aren’t exploited by cybercriminals. However, the implementation isn’t without challenges. Understanding the technicalities of public-key cryptography, managing DKIM keys, and ensuring the message remains unaltered during transit can be a bit confusing.

But don’t worry, there are best practices to ease the process, plus you don’t necessarily need to know the way DKIM works in detail to apply it to your emails. Regularly checking your DKIM record and ensuring it’s up to date is a great start. Also, consider using DKIM in conjunction with DMARC, another email authentication protocol, to further protect your domain.

Using DKIM to Prevent Email Spoofing

DomainKeys Identified Mail (DKIM) is a method used to validate the authenticity of an email. This method enables the recipient to confirm that the email was sent and authorized by the owner of a particular domain. The process involves using a cryptographic signature, which is an encrypted header attached to the message, to confirm the email’s genuineness and ensure it wasn’t altered during transmission. The recipient then uses a public key, located in the domain’s DNS DKIM record, to decrypt the DKIM signature and validate the message.

Domain-based Message Authentication Reporting & Compliance (DMARC), reinforces the DKIM protocol and the Sender Policy Framework (SPF) protocol to effectively strengthen defenses against email spoofing. DMARC makes sure there is a match between the visible ‘from’ address and the underlying IP address, thus preventing email spoofing. To successfully pass the DMARC checks, a message must either pass DKIM authentication, SPF authentication, or both.

However, there are common challenges in DKIM deployment. You may face difficulties such as:

  • Managing DKIM keys effectively
  • Keeping the private keys secure
  • Aligning the DKIM information with the ‘from’ address
  • Understanding the process (for non-technical users)
  • Handling emails that fail the DKIM checks

Despite these challenges, the benefits of DKIM for email authentication are substantial. It not only verifies the sender’s domain but also ensures the email hasn’t been messed with between being sent and delivered.

Why is DKIM Important for Email Marketing?

One of the major benefits of implementing DKIM is that it confirms your legitimacy as a sender, making your emails less likely to land in the spam folder. Of course, when it comes to email marketing campaigns, landing in the spam folder is the worst thing that can happen. This is just an additional step you should (need) to take to make sure your campaigns are fully effective and generate the ROI you were looking for.

Best practices for DKIM implementation include adding a DKIM record to your DNS whenever possible. This helps in authenticating mail from your domain and improving email deliverability. It’s a common challenge in DKIM deployment as it’s not a universally adopted standard. Yet, it’s compatible with existing email infrastructure and works well with other security protocols.

Lastly, DKIM has a significant impact on email authentication. It ensures your message hasn’t been altered, adding another layer of trust for the recipient. However, remember that while DKIM increases legitimacy, it doesn’t encrypt the contents of your message.


When it comes to securing your email and domain, both DKIM and SPF play crucial roles, albeit with slightly different purposes.

One of the benefits of implementing DKIM is that it verifies the sender and ensures the content hasn’t been tampered with during transmission. SPF, on the other hand, prevents spoofed messages.

Here are a few points to remember:

  • Implementing DKIM and SPF can be challenging due to how technical the process can be, but it’s essential for email security.
  • Misconceptions often arise about DKIM and SPF. They’re not alternatives, but complementary tools. Use both DKIM and SPF for the greatest protection.
  • Best practices for DKIM and SPF configuration involve setting up correct DNS records and regularly reviewing them.
  • Improper implementation of DKIM and SPF can lead to email delivery issues, damaging your domain’s reputation.
  • Proper implementation of DKIM and SPF can drastically improve your email deliverability


Now that we understand how DKIM and SPF work together, let’s discuss DMARC, and how it works with DKIM to protect your emails.

Common misconceptions might lead you to believe that these systems are interchangeable, but DMARC is actually the set of security rules that decides what to do when DKIM and SPF fail. Implementation challenges arise as DMARC requires careful configuration by your email server administrator.

The benefits of DMARC over DKIM are considerable. DMARC provides settings for failed DKIM validation: none, quarantine, or reject. This flexibility allows you to choose how to handle failed messages, whether that’s letting them through, quarantining them for review, or rejecting them outright.

In terms of industry best practices, many administrators opt for the quarantine setting. This allows them to inspect and learn from suspicious messages. Email service providers, such as Gmail, often use the reject setting, dropping millions of messages that fail validation to protect their users from phishing and hacking campaigns.

So, in summary, use all 3 (SPF, DKIM, and DMARC) to make sure your email marketing campaigns are as effective as possible.

What Is a DKIM Signature?

What Is a DKIM Signature_

The DKIM signature is an important component that ensures the integrity of your messages and shields you from phishing and malware attacks. It’s a unique hash created from various message components like the domain and body, encrypted with the sender’s domain private key.

In order to generate the signature, the sender uses the domain’s private key to encrypt the message, thereby creating a hash. Following this, the recipient’s email server employs the sender’s public key to encrypt the same elements from the message. The recipient then produces an encrypted result, known as a hash string, and matches it to the decrypted hash from the sender. If both strings match, then the DKIM verification is successful. However, if even a single character in the message is altered, the hash generated by using the public key to encrypt it will not match the one dispatched from the sender’s email server.

Yes, we understand this is very technical and honestly not necessary to know, but we want to give you all of the information in case this is important to you and your campaign. If the DKIM signature and selector (next topic) do not make sense to you, don’t worry, you can still implement DKIM relatively easily and know that it is protecting you on the backend.

What Is a DKIM Selector?

Building on our understanding of the DKIM signature, let’s take a closer look at the DKIM selector, a crucial element that helps locate the domain’s public key on the DNS server. During DKIM selector generation, it’s created as part of your public/private key pair and plays a pivotal role in understanding DKIM authentication.

Configuring DKIM for different email servers involves including this selector in the DKIM-Signature header of each email. When you send a test email to yourself, you can identify your DKIM selector in the “s” tag of this header.

However, there can be common issues with DKIM implementation. One problem is that the selector can get lost among numerous TXT entries on the DNS server. To avoid this, it’s best to maintain clear organization and regularly audit your entries.

As for managing DKIM keys, best practices suggest regularly rotating them to ensure security. You also need to update your selector whenever you change your keys. By maintaining these practices and understanding the role of the DKIM selector, you’re well on your way to securing your email domain.

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