Has it ever happened to you that you sent an email, but it never reached the recipient despite doing everything right? You authenticated your email-sending domain with SPF, DKIM, and DMARC, but somehow, your emails aren’t getting through.
Well, one of the reasons behind this could be that your authentication protocols aren’t correctly configured, particularly DKIM.
DKIM or DomainKeys Identified Mail is like a digital signature for your emails that helps establish the fact that an email indeed comes from your domain and hasn’t been tampered with along the way. If DKIM is up and running without a hitch, the recipient’s server will successfully verify the DKIM signature and trust that the email is untampered. But if it fails, the server might perceive it as untrustworthy and prevent it from making its way into the recipient’s mailbox, rendering all your email campaign efforts in vain.

But the good news is that you can easily fix DKIM failure and ensure that your emails reach their destination— the receiver’s inbox.
So, how do you do that? How do you prevent or fix DKIM failure and ensure smooth email delivery? This article will cover it all!
What is DKIM failure?
DKIM failure happens when the digital signature of an email fails to be verified on the recipient’s server. This simply means that the email cannot be authenticated as having been sent from your domain, and hence, the security system may flag it as suspicious.

In case DKIM fails, the email will be rejected or will land in the spam folder, thus causing poor email deliverability.
Here’s what happens:
Every DKIM-signed email has a cryptographic signature in its header. Upon reaching the recipient’s server, it checks that signature against a public DKIM key located in the sender’s DNS records. DKIM authentication fails if either no signature can be found or the one existing does not match; similarly, if the public key proves to be incorrect, authentication again fails.
What are the common reasons behind DKIM failure?
One thing’s certain: unless you identify the loopholes in our DKIM setup, your emails will continue to fail authentication, affecting deliverability and domain reputation.
Here are some of the common pitfalls that you should watch out for while setting up DKIM:

The DKIM record syntax is incorrect
If you set up DKIM manually without using a proper DKIM record generator, you may inadvertently introduce errors in your DNS records. Even the smallest mistakes, such as missing characters or poor formatting, can cause DKIM to fail.
DKIM alignment issues
If your domain has DMARC set up, DKIM should align with that. This means that the d= value within the DKIM signature should match the domain found in the ‘From’ address. When these do not match, the DKIM authentication can fail.
Skipping DKIM for third-party email services
While you might have authenticated your domain properly with DKIM, chances are that you did not take into account any third-party vendors or service providers, which is why your emails aren’t reaching the recipients’ inboxes. If you use services like Mailchimp or AWS to send emails on your behalf, they also need DKIM authentication. If you haven’t set it up for them, DKIM might fail.

Issues in server communication
Sometimes, the problem isn’t at your end, that is, with the DNS. Sometimes, the problem is with the email server itself.
What we mean to say here is that not all servers have DKIM enabled, and when you send an email from a server that doesn’t have DKIM or any signature is added whatsoever, the receiving server sees it as a red flag and stops it from entering the recipient’s mailbox.
The email content is changed after sending
When you send an email from a third-party vendor like a marketing service or a CRM platform, they sometimes add things like tracking links, footers, or disclaimers to your email. While these are harmless to the recipient, the receiving servers perceive them as a modification to the original mail that was sent from your end.
Since the whole point of DKIM is to confirm the authenticity of the email’s content, even the most minute changes can be flagged, leading to DKIM failure.

Your DNS is down or not working properly
DKIM functions by storing a unique key in your DNS settings. When you send an email, the recipient’s email server looks for that particular key in your DNS settings to check if the DKIM signature is valid. But if your DNS is down for some reason, like server maintenance, technical problems, or it’s simply not responding, the email server won’t be able to find it, thus failing the DKIM verification process.
Issues with OpenDKIM
Some email services use OpenDKIM, a free tool to verify DKIM signatures. If there is an issue with this tool or if it is not set up properly, such as incorrect file permissions or server connection issues, it can cause authentication failures.
What can you do to fix DKIM failure?
If your emails are all failing to get through, you might need to reassess your DKIM setup to find out what’s going wrong.

Here’s what you can do to fix DKIM failure:
- When generating a DKIM record, a DKIM generator is better; do not go about typing; instead, select a trusted site and simply copy-paste to avoid any typos.
- Make sure to thoroughly check your DKIM record. No matter how trivial, a minute error, space, or deleted character may even cause DKIM to fail completely.
- Make sure that you have enabled SPF and DMARC. These protocols work best together. In case DKIM fails, but if SPF is correct, DMARC can allow your mail to be delivered rather than reject it.
- Enable DMARC reports. These reports tell you which messages are failing DKIM verification and why.
- Monitor your DKIM failure reports regularly using an email security tool or an online DKIM checker to review your authentication results and spot errors early.
- When using a third-party email service, such as Google Workspace, Mailchimp, or SendGrid, make sure it supports DKIM and follow through with their requirements to configure the feature correctly.