DKIM Checker: What Is DKIM? DomainKeys Identified Mail Explained [Updated 2024]

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DKIM (DomainKeys Identified Mail) in a Nutshell

What is DKIM?

DomainKeys Identified Mail (DKIM) is an email authentication technique that allows the receiver to check that an email claimed to have come from a specific domain was indeed authorized by the owner of that domain. This is crucial in today’s digital age where email spoofing and phishing attacks are prevalent.

DKIM serves to enhance security by preventing email receivers from accepting forged or manipulated messages that could potentially harm users.

By utilizing DKIM signatures, it confirms the legitimacy of email senders, making it harder for malicious actors to spoof emails from trusted domains. This ensures that signed emails appear more legitimate to recipients and are less likely to be marked as spam, complementing other security protocols like SPF and DMARC, and is recommended for authentication by major ISPs.

The Basics of How DKIM Works

The functionality of DKIM revolves around the concept of “signing” emails. When an email is sent, it is signed using a private key unique to the domain from which it is sent. This signature is included in the email’s header, creating a DKIM signature header.

The corresponding public key, which resides in a DNS TXT record of the sending domain, is used by receiving email servers to verify the signature. This verification process checks that the email was not altered in transit and that it indeed comes from the specified domain, ensuring its authenticity.

To perform a DKIM check or DKIM lookup, the recipient’s email server retrieves the DKIM record from the DNS of the sender’s domain to find the public key needed to decrypt the signature. Successful verification adds a layer of trust, confirming that the email meets the domain’s DKIM policies and was not tampered with along the way.

In essence, DKIM helps establish a foundation of trust, ensuring that the identity of the sender can be confirmed and that the message integrity is intact. This is crucial for both senders and receivers in maintaining secure and reliable communication channels.

As we delve further into DKIM’s operational intricacies, we’ll explore more about how these mechanisms not only support but also strengthen the overall email security framework.

How to Utilize the Free DKIM Checker

Using the DKIM Record Checker to Validate Your DKIM Records

Validating your DKIM records is a vital step in ensuring that your email security setup is robust and functioning as intended. DKIM checkers are invaluable tools that simplify this process by providing a straightforward method to verify the integrity and correctness of your DKIM setup. Below is a step-by-step guide on how to use a free DKIM record checker effectively:

  1. Identify Your DKIM Selector: Before you can check your DKIM record, you need to know the DKIM selector. This is typically specified by your email service provider or configured when setting up DKIM. The selector is a crucial component of the DKIM record that helps pinpoint which DNS record holds your public key.
  2. Locate a Free DKIM Checker Tool: Numerous online tools offer free services to check DKIM records, such as Octeth’s Free DKIM Checker Tool, MXToolbox, DNSChecker, or tools specific to email service providers. These platforms provide a DKIM lookup service that you can use without any additional cost.
  3. Enter the Required Information: On the DKIM checker tool, you will usually need to enter your domain name and the DKIM selector. This information directs the tool to retrieve the correct DNS TXT records that contain your DKIM public keys.
  4. Run the DKIM Check: After entering the necessary details, initiate the check. The tool will perform a DKIM lookup in your DNS records to find and display the DKIM record. It typically shows whether the DKIM record is correctly set up and provides details on any issues detected.
  5. Analyze the Results: The output will often include the DKIM record syntax, the public key, and any discrepancies or validation errors. Look for key elements such as a valid DKIM signature, proper alignment with the sending domain, and the overall status indicating whether the DKIM validation passed or failed.
  6. Make Necessary Adjustments: If the checker indicates issues with your DKIM record, consult with your domain’s DNS administrator to make the required changes. This might involve correcting the DKIM signature, adjusting the DNS TXT record, or reconfiguring the DKIM selector.
  7. Re-test After Adjustments: Once adjustments are made, it is essential to re-run the DKIM test to confirm that all issues are resolved and your DKIM record is correctly validated.

Using a DKIM checker not only helps in maintaining the security and reliability of your outgoing email messages but also enhances email deliverability by ensuring your emails are less likely to be marked as spam by recipient servers.

Regular checks using a DKIM record checker can help safeguard your email communication against spoofing and phishing, fortifying your email’s credibility and trustworthiness.

Understanding DKIM Records and Keys

What Are DKIM Keys and Records?

DKIM keys and records are foundational elements in the DKIM email authentication framework. A DKIM key consists of a public-private key pair. The private key is used by the sending mail server to digitally sign parts of the email and headers. The corresponding public key is published in the DNS records of the sender’s domain, allowing recipient mail servers to verify the authenticity of the signed email.

A DKIM record, on the other hand, is a specific type of DNS TXT record that stores the public key and additional DKIM configuration details. This record enables the receiving email server to locate the public key and use it to decrypt the signature from the email header, thus verifying that the email has not been tampered with and is indeed from the stated domain. The DKIM record contains several important elements including:

  • v=DKIM1; indicating the version of DKIM used.
  • p= the public key necessary for verifying the signature.
  • s= the scope of emails that the record is intended to cover, often set to “*” for all emails.
  • h= optional, specifying the hashing algorithm used.

How to Find a DKIM Signature

To find a DKIM signature within an email, follow these steps:

  1. Open the Email: Start by opening the email whose DKIM signature you want to inspect.
  2. View Source or Original Message: Most email clients have an option to ‘View Source’ or ‘Show Original’ which displays the full raw data of the email.How to view the source of the email in Gmail
  3. Look for the DKIM Signature Header: Scroll through the header section or search for “DKIM-Signature”. This field contains the actual digital signature, created by the sender’s email server.DKIM signature header displayed above.

The DKIM signature header will typically include several tagged values like v=, a=, q=, d=, s=, among others, detailing everything from the version of DKIM and the algorithm used to the domain and selector identifying the specific DKIM record used for signing.

How to Check DKIM Record in Your DNS

Checking the DKIM record in your DNS is a straightforward process:

  1. Identify Your Domain and Selector: You need your domain name and the selector used for DKIM. The selector is often provided by your email service provider or IT department. The domain name is defined in “d=” parameter and the selector is defined in “s=” parameter.
  2. Use a DNS Lookup Tool: Tools like MXToolbox, DNSChecker, or command-line tools such as dig or nslookup can be used. For instance, if your selector is s1 and your domain is, you would check for
  3. Run the Lookup: Enter the full name (e.g., into the DNS tool. Select TXT as the type of record you are looking for, and perform the search.
  4. Analyze the Results: The output should display the DKIM TXT record, showing the public key and other DKIM settings. Ensure the record is correct and matches what is expected for your DKIM configuration.

Advanced DKIM Topics

How to Analyze DKIM Selector From DMARC Aggregate Reports

DMARC (Domain-based Message Authentication, Reporting & Conformance) aggregate reports are crucial tools for domain owners to understand how their emails are being handled by receiving servers and to identify potential authentication issues. These reports also include detailed information about the DKIM selectors used in email authentication, which can provide valuable insights.

  1. Obtain DMARC Aggregate Reports: These reports are typically sent by email receivers to the address specified in your DMARC DNS record under the “rua” tag. Ensure your DMARC record is set up to receive these reports.
  2. Locate the DKIM Selector Information: Within the DMARC aggregate reports, look for sections detailing DKIM results. These sections will include the DKIM selector that was used to sign the email. This selector is critical as it ties back to the specific DKIM record used during the authentication process.
  3. Analyze Selector Usage and Performance: By analyzing the selectors mentioned in the reports, you can assess which selectors are being used most frequently and how effectively they are performing in terms of passing DKIM authentication. This analysis can help you determine if specific selectors need updates or modifications.
  4. Make Informed Adjustments: If a particular DKIM selector shows a high rate of failure, it might indicate an issue with how emails are being signed or with the DNS record itself. Based on this analysis, you can make targeted adjustments to improve your email authentication setup.

Analyzing DKIM selectors from DMARC aggregate reports not only helps in ensuring that your email authentication is functioning correctly but also aids in optimizing your email delivery and sender reputation.

DKIM record check via “nslookup” From the Command Line

Using “nslookup,” a command-line tool available in most operating systems, you can manually run DKIM record check in the DNS and make a DKIM record lookup. This method is particularly useful for administrators and technical users who prefer direct interaction with server systems.

  1. Open Command Line: Start by opening your command prompt or terminal.
  2. Run nslookup: Enter the command nslookup -type=txt <selector>._domainkey.<>. Replace <selector> with your DKIM selector and <> with your domain name.
  3. Analyze the Output: The output will display the TXT records for the specified selector. Look for a string that starts with “v=DKIM1;” which indicates the DKIM record which includes the DKIM public key. This record should contain your public key and potentially other tags related to DKIM setup.
  4. Verify the Record Details: Ensure that the public key and other details in the DKIM record are correct and aligned with your email security policies. Any discrepancies should be addressed to ensure that your DKIM is set up properly.
  5. Troubleshoot as Needed: If the record does not appear or if the details are incorrect, you may need to troubleshoot your DNS settings or consult with your DNS provider.
Checking DKIM via “nslookup” From the Command Line

Using nslookup for checking DKIM records provides a direct and efficient way to ensure that your DKIM setup is accurate and functioning as expected. This hands-on approach can be crucial for immediate troubleshooting and for regular maintenance of your domain’s email security infrastructure.

DKIM Integration with Other Email Security Practices

Why You Need DKIM, DMARC, and SPF Checks

In the landscape of modern email communication, ensuring the authenticity and integrity of emails is crucial for protecting against phishing, spoofing, and other malicious activities. Integrating DKIM (DomainKeys Identified Mail), DMARC (Domain-based Message Authentication, Reporting & Conformance), and SPF (Sender Policy Framework) provides a robust defense mechanism for your email systems.

  • Comprehensive Email Validation: While DKIM provides a way to verify that an email was not altered and truly comes from the stated domain, SPF checks if the email comes from a valid server of the sender’s domain. DMARC ties these protocols together by specifying a policy on how to handle emails that fail these checks, enhancing the security and deliverability of emails.
  • Enhanced Trust and Deliverability: Using all three checks increases the likelihood that your emails will be trusted by recipient servers and thus delivered successfully. It significantly reduces the chance of your emails being flagged as spam or phishing attempts, which is vital for maintaining your domain’s reputation.
  • Alignment with Best Practices: Major email providers and organizations around the world recommend the adoption of these standards as part of best practices in email security. This alignment not only improves security but also ensures compatibility and effectiveness across diverse email systems.

DKIM and Its Relationship to DMARC and SPF

DKIM, SPF, and DMARC are complementary technologies that each address different aspects of email security:

  • DKIM signs your emails to prove they have not been tampered with and that the sender’s domain is authentic.
  • SPF allows the domain owner to define which email servers are permitted to send mail for their domain, helping to prevent email spoofing.
  • DMARC uses the results of DKIM and SPF evaluations to provide instructions to receiving mail servers on what to do if these checks fail (e.g., reject the message, quarantine it, or pass it with a warning). It also provides a way for recipients to report back to senders about messages that pass and/or fail DMARC evaluation.

Together, these protocols fortify email security by providing multiple layers of verification, thereby making it difficult for attackers to exploit email systems.

Is DKIM Part of the DMARC Protection?

Yes, DKIM is a crucial component of DMARC protection. DMARC policies utilize the results of DKIM signature checks to determine how to handle incoming emails. If an email fails DKIM verification but passes SPF, or vice versa, DMARC policy settings dictate the next steps:

  • None: The email will be delivered normally, despite the failure.
  • Quarantine: The email could be placed into the spam/junk folder.
  • Reject: The email will be rejected outright.

DMARC requires either a DKIM or SPF pass to consider the email authenticated, underlining the importance of setting up DKIM correctly as part of broader DMARC protection strategies.

Integrating DKIM with SPF and DMARC not only enhances the security of your email environment but also ensures that your communications are trusted, verified, and more likely to reach their intended recipients without interference. This integration is key to building a resilient email defense system against the increasingly sophisticated email threats faced by organizations today.

Comparative Analysis of Email Authentication Methods


DKIM (DomainKeys Identified Mail) and SPF (Sender Policy Framework) are both essential for email security, but they serve different purposes and operate in distinct ways:

  • Functionality: DKIM provides a way to validate a message was not altered from the time it was sent, through a digital signature linked to the sender’s domain. SPF, on the other hand, verifies the sending mail server itself, ensuring that the email comes from a server authorized by the domain owner.
  • How They Work: DKIM uses a pair of keys, one private and one public. The sending server signs the email with the private key, and the recipient verifies this signature using the public key published in the sender’s DNS. SPF works by having the domain owner publish a list of servers that are permitted to send emails on behalf of the domain, which receiving servers check against.
  • Limitations: DKIM does not prevent someone from sending emails from a server that might be temporarily considered legitimate. SPF can fail in scenarios where emails are forwarded, as the initial sending server may not be on the recipient’s SPF record.

Each of these methods covers aspects of security that the other does not, making them complementary rather than standalone solutions.


DKIM and DMARC (Domain-based Message Authentication, Reporting, and Conformance) are closely related but serve different roles in the email authentication landscape:

  • Role of DKIM: As noted, DKIM ensures the integrity of the message content from the point it leaves the sending server to when it is opened by the receiver.
  • Role of DMARC: DMARC leverages the results of DKIM and SPF checks to enforce policies on how to handle emails that fail these checks. It also provides a framework for sending reports on these failures back to the sender, helping administrators understand and improve their email security posture.
  • Operational Context: While DKIM signs the messages, DMARC tells the recipient what to do if an email fails the DKIM or SPF check. DMARC can instruct receiving servers to reject emails outright if they fail, something neither DKIM nor SPF can do on their own.

DMARC is a protocol that helps domain owners to use their DKIM and SPF records more effectively as part of a comprehensive strategy against email fraud.

Technical Insights into DKIM

Do I Need a Certificate to Run DKIM?

Unlike SSL/TLS, DKIM does not require a certificate issued by a certificate authority. DKIM utilizes a pair of cryptographic keys:

  • Private Key: Held securely by the sender, used to create the DKIM signature.
  • Public Key: Published in the DNS TXT records of the sender’s domain, used by recipients to verify the signature.

The “certificate” in DKIM is essentially the public key itself, which is openly available and does not require validation by a third party. This setup allows for secure verification of email authenticity without the complexity and cost associated with traditional certificates.

Limitations and Potential Pitfalls of DKIM

While DKIM is a powerful tool for email authentication, it has several limitations and potential pitfalls:

  • Does Not Encrypt: DKIM does not encrypt emails; it only verifies their source and integrity. Sensitive information in emails should be protected through other means, such as end-to-end encryption.
  • Dependent on Configuration: DKIM’s effectiveness is heavily dependent on correct DNS setup and key management. Poorly managed keys or DNS records can lead to failed verifications.
  • Vulnerability to Certain Attacks: While DKIM protects against direct tampering, it does not prevent attacks where emails are intercepted and redirected without modification.

Understanding these technical aspects and challenges of DKIM is essential for implementing and maintaining it as part of a comprehensive email security strategy. These insights help ensure that DKIM provides the intended level of protection without introducing new vulnerabilities into the organization’s email practices.


DomainKeys Identified Mail (DKIM) is a pivotal email authentication technique that validates the sender’s domain and ensures the integrity of messages throughout their delivery. By affixing a digital signature to emails and verifying it against a public key in the sender’s DNS records, DKIM confirms the email’s authenticity and unchanged status, thus playing a critical role in thwarting email spoofing and phishing.

Although DKIM doesn’t provide end-to-end encryption or directly impact spam filtering, it is crucial for improving deliverability and sender reputation.

For comprehensive security, it’s advisable to integrate DKIM with SPF and DMARC, forming a robust defense against email-related threats and enhancing the security and reliability of email communications in the face of evolving cyber challenges.

Frequently Asked Questions

Does DKIM Give My Messages End-to-End Encryption?

No, DKIM (DomainKeys Identified Mail) does not provide end-to-end encryption for messages. Its primary function is to authenticate the source of an email and ensure that the email’s content has not been altered during transit. DKIM does this by allowing the sender to attach a digital signature to the email, which the recipient’s server verifies using a public key published in the sender’s DNS. For securing the contents of an email against interception or eavesdropping, other technologies such as PGP (Pretty Good Privacy) or S/MIME (Secure/Multipurpose Internet Mail Extensions) should be used, which are designed to encrypt messages end-to-end.

How Many DKIM Records Can I Have?

You can have multiple DKIM records for a single domain, which is particularly useful if different servers or services send emails on behalf of your domain. Each DKIM record is associated with a unique selector, a mechanism that allows you to differentiate between the keys and configurations used by various email sources. This flexibility enables you to manage email authentication more effectively, such as by rotating keys regularly or tailoring configurations to specific servers or services. There’s no strict technical limit to the number of DKIM records you can implement, but managing them efficiently is crucial to maintaining a secure and organized email authentication system.

If I Have an SPF, Do I Have to Implement DKIM?

While having an SPF (Sender Policy Framework) helps verify the sending server, implementing DKIM (DomainKeys Identified Mail) is also recommended for comprehensive email security. DKIM ensures the content of the email remains unchanged and authenticates the sender’s domain, which SPF alone does not cover. Using both SPF and DKIM improves email deliverability and reputation, significantly reducing the likelihood of your emails being marked as spam. Thus, for enhanced security and better deliverability, it’s advisable to implement both protocols along with DMARC for full email authentication and policy enforcement.

Can DKIM alone guarantee my emails won’t go to spam?

No, DKIM alone cannot guarantee that your emails won’t be marked as spam. While DKIM helps authenticate the sender and ensure the integrity of the email content, it is just one component of what email servers consider when determining spam. Other factors, such as the sender’s reputation, the content of the email, and the recipient’s specific email settings, also play significant roles. For optimal email deliverability, it’s recommended to use DKIM in conjunction with SPF (Sender Policy Framework) and DMARC (Domain-based Message Authentication, Reporting & Conformance), which together provide a stronger defense against being flagged as spam by enhancing the overall trustworthiness and legitimacy of your emails.

How often should I update my DKIM keys?

It’s advisable to rotate your DKIM keys periodically to maintain a high level of security, particularly if you suspect that your private key has been compromised. While there is no set rule on the frequency of key rotation, a common practice is to change them annually or biannually. Regular updates help prevent potential security breaches and ensure the integrity of your email authentication process. Remember, each time you update your DKIM keys, you must also update your DNS records with the new public key to ensure that email verification continues to function correctly without disruptions to your email delivery.

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