DKIM failures can harm your email deliverability and sender reputation. Here’s why they happen and how to fix them:

  1. Incorrect DKIM Record Setup: Issues like wrong DNS zones, syntax errors, or missing public keys prevent verification.
  2. DKIM Key Problems: Mismanagement, like mismatched records or not rotating keys, disrupts authentication.
  3. DNS Server Problems: Downtime or slow propagation can block access to your DKIM public key.
  4. Email Content Changes: Modifying emails after signing (e.g., adding headers or footers) breaks the DKIM hash.
  5. Email Service Setup Errors: Misconfigured email services overwrite DKIM settings, causing failures.

Quick Fixes:

  • Double-check DNS records and syntax.
  • Rotate keys regularly and ensure consistency.
  • Monitor DNS uptime and propagation.
  • Avoid altering signed emails.
  • Ensure your ESP handles DKIM correctly.

Why does DKIM fail? DKIM Failure Types, Examples and Fixes

1. Incorrect DKIM Record Setup

A poorly configured or missing DKIM DNS record can stop servers from accessing your public key, making it impossible to verify your domain.

Here are the key areas to check:

DNS Zone and Selector Issues
The DKIM record must be placed in the correct DNS zone with the appropriate selector name. If it's in the wrong spot, servers won't find the public key.

Syntax Errors
Every tag and parameter in the record must comply with the DKIM specification. Even small syntax mistakes can cause problems.

Missing Components
Make sure the record includes the public key and all required tags. Leaving out any of these elements will disrupt the verification process.

Double-check the DNS zone, selector, syntax, and ensure the public key is present. Next, we'll look at how issues with the DKIM key itself can lead to authentication failures.

2. DKIM Key Problems

Once you've set up your records correctly, the next challenge is managing your DKIM keys. Poor key management can lead to verification failures and hurt email deliverability.

Key Rotation
It's important to rotate your DKIM keys on a regular basis to maintain security.

Record Consistency
Make sure your DNS DKIM records match the private keys precisely. Even small mismatches can cause authentication issues.

Next, we'll look at how problems with DNS servers can interfere with DKIM checks.

3. DNS Server Problems

Once you've ensured key consistency, the next critical step is maintaining DNS availability. Mail servers depend on DNS lookups to retrieve DKIM public keys. If your DNS is down or slow to update, verification can fail.

Downtime
When your DNS provider experiences downtime, mail servers can't access your public key. This can lead to signature failures, causing emails to bounce or be flagged as spam.

Propagation Delays
DNS record updates don't happen instantly. If servers are referencing outdated records, they won't be able to verify signatures correctly.

How to avoid DNS issues:

  • Use multiple DNS providers spread across different regions
  • Set up tools to monitor DNS uptime and receive alerts for issues
  • Regularly query your DNS from various locations to ensure your public key is accessible

4. Email Content Changes

Any changes to an email's content after it’s signed - like adding headers, adjusting formatting, or appending footers - will break the DKIM hash, potentially causing authentication issues.

How to Prevent This

  • Avoid making automated changes to emails after they’ve been signed.
  • Use forwarding methods that keep the headers and body untouched.

Additionally, misconfigured email services can lead to authentication errors, so ensure proper setup.

5. Email Service Setup Errors

Your email service provider (ESP) plays a crucial role in maintaining DKIM signatures, which directly impact email deliverability and reputation. If your ESP is misconfigured, it can overwrite DKIM settings and disrupt these signatures. Once you've secured your headers and content, double-check that your ESP is properly handling DKIM.

Tips to Avoid Issues

  • Make sure DKIM signing is enabled in your ESP and aligns with the selector in your DNS record.
  • Regularly review your ESP's DKIM configuration to catch any changes or inconsistencies.
  • Use tools like Bounceless's API to clean your email list by removing invalid addresses, spam traps, and duplicates.

How to Fix DKIM Failures

Once you've identified DKIM failures, here are some steps to address them:

  • Use tools like Bounceless's domain validation to review and verify your DNS and domain settings regularly.
  • Ensure the email content remains consistent from the time it's signed to when it's delivered. Any changes can break the DKIM signature.
  • Clean up your mailing list by removing invalid addresses and spam traps with Bounceless. This helps maintain DKIM integrity [2].

Conclusion

Following these steps will help keep your domain's email signatures intact, improve deliverability, and protect your sender reputation. Regularly checking your DKIM setup can catch potential issues early, keeping your campaigns running smoothly. Paying attention to these basics ensures reliable email delivery and maintains your domain's credibility.

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