What is DKIM? A beginner’s guide
Sendmarc makes DKIM simple – helping you set up, manage, and monitor authentication so your messages stay trusted and secure.
But what is DKIM in email? DomainKeys Identified Mail (DKIM) verifies that your organization’s emails haven’t been tampered with during transit.
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What is DKIM: DKIM basics
DKIM records act like a digital passport for your business’s emails. It allows email servers that receive your company’s messages to verify that they haven’t been altered along the way.
When your organization sends an email, DKIM attaches a digital signature. The recipient’s server checks this signature using information from your business’s DNS records. If everything matches, your company’s email is verified as authentic.
Understanding “What is DKIM in email” means knowing how digital signatures protect your email integrity.
What is DKIM & how does it work?
When IT teams ask, “What is DKIM in practice?”, the answer lies in how cryptographic signatures confirm message authenticity.
DKIM allows receiving email servers to check whether a message has been tampered with in transit.
Here’s how it works:
- When your organization’s email server sends a message, it attaches a DKIM signature to the header. This signature is a cryptographic hash, which is generated using a private key.
- The receiving server looks up the domain’s public DKIM key in the DNS and uses it to verify the signature.
- If the signature matches, the message is verified as authentic and unchanged. If it doesn’t, the message might be flagged or rejected, depending on your business’s email security policy.
DKIM is a core component of a secure email strategy and works alongside Sender Policy Framework (SPF) and Domain-based Message Authentication, Reporting, and Conformance (DMARC) to protect your company’s domain from abuse.
Want help setting up DKIM correctly? Book a demo with a Sendmarc expert to see how we streamline DKIM, SPF, and DMARC implementation.
What is DKIM & why does it matter?
Implementing DKIM is essential for strengthening email security and maintaining domain reputation. Without DKIM, cybercriminals can attack your organization’s domain, putting both your business and its clients at risk.
Key benefits of DKIM:
- Prevent email tampering: DKIM helps protect recipients from MitM attacks
- Improve email deliverability: Authenticated messages are more likely to reach inboxes instead of being marked as Spam or Junk
- Build customer trust: Recipients are more likely to engage with emails that are verified as secure and legitimate
Ultimately, learning “What is DKIM” helps domain owners see how it directly improves trust, deliverability, and security.
What is DKIM & how does it compare?
What is DKIM: DKIM vs. SPF
- DKIM: Authenticates the contents and headers of an email by applying a digital signature that can be verified by the recipient
- SPF: Validates whether the sending email server is authorized to send on behalf of the domain, but doesn’t verify the contents of the message
What is DKIM: DKIM vs. DMARC
- DKIM: Confirms the authenticity and integrity of the email using a cryptographic signature
- DMARC: Builds on both DKIM and SPF to enforce policies and tell receiving servers how to handle emails that fail authentication
So, when domain owners compare protocols and ask, “What is DKIM and is it better than SPF or DMARC?”, the takeaway is that all three work best together.
Together, DKIM, SPF, and DMARC provide a layered defense that protects your company’s domain and improves email performance.
Need help implementing all three protocols the right way? Book a demo with us to secure your organization’s email from spoofing and improve deliverability.
What is DKIM: How to ensure it's active
Verifying that DKIM is active and correctly working is a critical part of safeguarding your business’s email domain. Your company can confirm this using tools like Sendmarc’s DKIM lookup and header analysis.
- DKIM lookup: Use this tool to check whether your organization’s public DKIM key is published correctly in its DNS.
- Header analysis: After sending an email from your business’s system, run the message through Sendmarc’s header analysis tool. This reveals:
- Whether the private key is present
- How recipient email servers evaluate the DKIM record
These tools make it easy to confirm that DKIM is protecting your company’s email and that its messages are properly authenticated.
Ensure your emails are protected and authenticated from the start.