Summary
DKIM (DomainKeys Identified Mail) is a critical email authentication standard that helps protect your domain from spoofing and phishing by allowing the receiver to verify that an email was indeed sent and authorized by the domain owner. When DKIM fails, it can significantly impact your email deliverability, leading to messages being rejected or sent to spam folders. Common causes range from incorrect DNS record configuration to issues with how your email service provider (ESP) signs outgoing emails, particularly when dealing with subdomains. Proper setup, especially for subdomains, is essential to ensure email integrity and trust.
Key findings
- DNS conflicts: A primary cause of DKIM failure is having multiple or conflicting TXT records for the same DKIM selector in your DNS, particularly for a single domain.
- Subdomain setup: Each subdomain often requires its own distinct DKIM record, which should be configured separately from the main domain's record.
- Provider behavior: Some email service providers (ESPs) might behave unpredictably when multiple keys are present or might not consistently use the intended DKIM key for signing, particularly for subdomains.
- Impact on DMARC: DKIM failures directly impact DMARC authentication, even if SPF passes, leading to reduced email trustworthiness and potential delivery issues. For more on DMARC authentication failures, see our guide on why DMARC authentication fails when SPF and DKIM pass.
Key considerations
- Verify DNS records: Always double-check your DNS entries for DKIM. Ensure there are no duplicate TXT records for the same selector and that the record is correctly published.
- Separate subdomain records: When sending from a subdomain, create a unique DKIM record specifically for that subdomain. This prevents conflicts with the primary domain's DKIM. Learn more about setting up email subdomains and their DNS records.
- Understand ESP behavior: Be aware of how your email service provider handles DKIM signing, especially when using multiple domains or subdomains. Some providers might have specific requirements or limitations.
- Troubleshoot systematically: If DKIM fails, systematically check DNS propagation, record syntax, and ensure your sending system correctly applies the signature. A useful resource on general DKIM failure causes is AutoSPF's guide on why DKIM fails.
What email marketers say
Email marketers often face challenges with DKIM setup, particularly when integrating new subdomains or migrating email services. Their experiences highlight common pitfalls like conflicting DNS records and the need for meticulous configuration. Many find that minor errors can have significant impacts on email deliverability, emphasizing the importance of clear guidance and troubleshooting steps for these technical aspects.
Key opinions
- Unexpected failures: Marketers frequently report DKIM failures even when SPF and DMARC seem correctly configured, often after seemingly minor changes like adding a new record.
- Conflicting records: A common mistake involves adding multiple DKIM TXT records for what's perceived as the same domain, which can cause authentication to fail unpredictably.
- Subdomain complexity: Setting up DKIM for subdomains is a source of confusion, with marketers often unsure whether separate records are required or how they interact with the main domain's DKIM.
- Documentation gaps: Some marketers find that existing documentation or setup guides from providers can sometimes omit crucial steps or nuances, leading to failed configurations.
Key considerations
- Careful record additions: Exercise caution when adding new DNS records, especially DKIM, to avoid inadvertently creating conflicts with existing configurations.
- Dedicated subdomain records: It is generally advisable to set up dedicated DKIM records for each subdomain you use for sending. This ensures proper alignment and authentication. Consider how DKIM can be set up on a subdomain.
- Test thoroughly: After any DKIM configuration change, send test emails and use authentication checkers to confirm the setup is working as expected. This helps identify issues early.
- Review DMARC reports: Regularly reviewing DMARC reports is crucial, as they provide insights into DKIM authentication failures, including those related to subdomains. An example of a marketer discussing this can be found on Spiceworks Community.
Marketer view
Marketer from Email Geeks describes encountering a DKIM failure for their primary domain in Google Workspace, even with SPF and DMARC appearing to be correctly configured. They sought immediate community advice.
Marketer view
Marketer from Spiceworks Community observes that setting up SPF and DKIM records individually for each domain and subdomain is crucial, although some configurations might allow for redirection to avoid creating unique records for every subdomain.
What the experts say
Email deliverability experts highlight that DKIM failures often stem from misconfigurations in DNS records, particularly conflicting entries or incorrect setup for subdomains. They stress the importance of understanding how email service providers implement DKIM and the implications of misconfigurations on DMARC authentication. Their insights underscore the need for precise technical execution and careful monitoring to ensure email integrity.
Key opinions
- DNS accuracy: Experts consistently emphasize that incorrect or conflicting DNS TXT records are a primary reason for DKIM failure, making careful DNS management crucial.
- Undefined outcomes: When DNS records are misconfigured, such as having duplicate DKIM entries, email receivers can interpret them in various ways, leading to unpredictable authentication results.
- Subdomain independence: A DKIM record for a specific subdomain should not interfere with the main domain's DKIM record, provided they are correctly named and distinct.
- Provider signing variability: Even with correct DKIM setup for subdomains, some major email service providers might exhibit unpredictable behavior regarding which DKIM key they use for signing outbound mail.
Key considerations
- Isolate subdomain records: Always set up separate DKIM keys and DNS records for each subdomain, ensuring they are distinctly named to avoid conflicts with the parent domain. For more on this, see how to configure SPF, DKIM, and DMARC for subdomains.
- Verify private key use: Ensure your sending server or ESP is correctly using the designated private key to sign outgoing emails. Misalignments here often cause DKIM failures.
- Monitor DMARC reports closely: Leverage DMARC reports (RUA and RUF) to gain detailed insights into DKIM authentication failures, which helps diagnose specific issues. This is especially true when dealing with platforms like Google Workspace. For more on Google Postmaster Tools, see our ultimate guide to Google Postmaster Tools V2.
- Consult ESP documentation: Refer to your email service provider's specific documentation for DKIM setup, as they may have unique requirements or recommended practices. Spamresource.com offers general advice on maintaining a clean sender reputation, which DKIM is crucial for.
Expert view
Expert from Email Geeks advises checking DNS records immediately if DKIM is failing, specifically looking for duplicate or conflicting TXT entries for the DKIM selector, which can cause unpredictable results.
Expert view
Expert from Spamresource states that maintaining a clean sender reputation is crucial for deliverability, and DKIM plays a significant role in proving email authenticity to recipients, thus building trust.
What the documentation says
Official documentation from various email service providers and security entities consistently outlines that DKIM is a critical authentication method to verify email legitimacy. They detail that failures often arise from precise technical errors, such as incorrect DNS entries, missing signatures, or alignment issues. The documentation stresses the sequential importance of setting up SPF and DKIM before DMARC and highlights the need for meticulous configuration to ensure proper email delivery and security.
Key findings
- Purpose of DKIM: DKIM is presented as an authentication method to confirm that emails originate from legitimate domains and have not been tampered with in transit.
- Common failure points: Documentation frequently lists missing or incorrect DKIM signatures, minor syntax errors in DNS records, and alignment inconsistencies between the signing domain and the 'From' header as primary reasons for failure.
- Prerequisite for DMARC: It is consistently recommended to set up SPF and DKIM before implementing DMARC to avoid immediate email delivery issues and to ensure proper reporting.
- Observational DMARC policies: When initially implementing DMARC, documentation often advises starting with a relaxed policy (e.g., p=none) to observe authentication failures without immediately rejecting emails.
Key considerations
- Strict adherence to syntax: Pay close attention to every character and the formatting of your DKIM DNS records, as even the smallest errors can lead to validation failures.
- Domain and subdomain specificity: Ensure that DKIM verification details are specific to your domain and subdomains, as these are tied to the associated private keys used for signing. Learn more about common DKIM selectors.
- Prioritize SPF and DKIM: Always establish robust SPF and DKIM configurations before progressing to DMARC policies to minimize delivery disruptions.
- Continuous monitoring: Utilize DMARC reports to continuously monitor DKIM authentication results and proactively address any failures. Mailjet's blog on setting up DKIM provides a step-by-step guide that emphasizes this.
Technical article
AutoSPF documentation highlights that even the smallest mistakes, such as missing characters or poor formatting, can cause DKIM to fail, alongside more complex DKIM alignment issues.
Technical article
Mailjet documentation recommends starting with a relaxed DMARC policy when first implementing it, to allow observation of which emails are failing authentication without immediate rejection.
Related resources
7 resources
Related pages
Can DKIM be set up on a subdomain, and which domain should be used for signing?
How to set up email subdomains and what DNS records are required?
How to fix DKIM from domain mismatch and understand DMARC risks?
Why is my DKIM body hash failing and how do I fix it?
Decoding DKIM temperror: what it is and how to fix it
A simple guide to DMARC, SPF, and DKIM
Why are Microsoft Office 365 DKIM signatures failing and how to fix it?
Why is DKIM failing at some ISPs but not others, and how can I fix it?
How to fix “DKIM record published no DKIM record found” errors
Why Your Emails Fail: Expert Guide to Improve Email Deliverability [2025]
