Summary
DKIM failures at some ISPs but not others arise from a confluence of factors, primarily related to DNS configuration, content integrity, ISP-specific policies, and encoding inconsistencies. DNS misconfigurations, such as incorrect records, wildcards, or server issues, lead to propagation and caching inconsistencies among ISPs. Content alterations during transit, character encoding variations, and improper DKIM setup, including selector mismatches and insufficient key lengths, also contribute. Moreover, ISPs' varying strictness in DNS validation, policies, and DMARC enforcement exacerbates the problem. Resolving these issues requires meticulous DNS verification, standardized encoding practices (e.g., UTF-8), adherence to ISP-specific requirements, utilization of email authentication validation tools, content integrity measures, and consistent monitoring.
Key findings
- DNS Misconfiguration: Incorrect DNS records, improper DNS server setup, wildcard entries, and propagation delays are common causes of DKIM failures.
- Content Alteration: ISPs modifying email content (headers/footers) during transit invalidates the DKIM signature; use TLS and avoid unnecessary intermediaries.
- Encoding Issues: Inconsistent character encoding leads to hashing mismatches and DKIM failures; standardize encoding (UTF-8).
- DKIM Setup Errors: Incorrect selector names, typos in DNS records, and insufficient key lengths cause failures; validate DKIM DNS records and keys.
- ISP-Specific Policies: Stricter ISP policies (e.g., Yahoo) require specific key lengths and DNS record propagation.
- Authentication Mismatch: Inconsistencies between sending practices, IP addresses, and email authentication records (DKIM, SPF, DMARC) lead to failures.
- Header Alignment: Misalignment between the 'header from' domain and DKIM/SPF records triggers DKIM failures and DMARC issues.
- DNS Propagation/Caching Differences: ISPs have varying DNS caching intervals, leading to failures when changes aren't reflected quickly.
Key considerations
- DNS Validation: Regularly validate and correct DNS records using dedicated tools (e.g., DNS Viz, XNND, GlockApps) to ensure proper propagation.
- Content Integrity: Implement end-to-end encryption (TLS) and minimize email content alteration by intermediaries.
- Encoding Standardization: Enforce consistent character encoding (UTF-8) to avoid signature mismatches.
- Key Length Compliance: Use DKIM keys of sufficient length (2048 bits) that comply with major ISP requirements.
- DKIM Implementation Checks: Verify the correctness of the DKIM setup, including proper selector names and DNS record syntax.
- Policy Alignment: Align sending practices and email infrastructure with authentication records (DKIM, SPF, DMARC).
- ISP Policy Awareness: Stay informed about the specific email authentication policies of major ISPs (Yahoo, Gmail, Outlook).
- Regular Testing: Test DKIM with various email clients and ISPs to identify issues early and ensure consistent performance.
What email marketers say
8 marketer opinions
DKIM failures at some ISPs but not others often stem from issues like content alteration in transit, incorrect DKIM setup, stricter ISP policies, DNS propagation inconsistencies, signature mismatches, or misalignment of authentication records. Resolving these requires verifying DNS configurations, standardizing character encoding, validating DKIM keys, ensuring proper SPF and DMARC alignment, testing with various providers, and maintaining good sender reputation.
Key opinions
- Content Alteration: ISPs might modify email content (headers/footers), invalidating the DKIM signature. Use TLS and avoid unnecessary intermediaries.
- Configuration Errors: Incorrect DKIM selector names or typos in DNS TXT records are common. Use validation tools to check DNS settings.
- ISP Policies: Some ISPs (e.g., Yahoo) have stricter policies; check key length and ensure DNS records propagate fully.
- Signature Mismatch: DKIM failures occur when the signature doesn't match the content due to encoding, signature process or DNS problems. Testing can help isolate the problem.
- DKIM Validation: Use online tools to validate DKIM DNS records and keys. Functional verification is important.
- DNS Configuration: Ensure proper DNS configurations, including matching DKIM and SPF records to sending domains.
- Authentication Records: Check if sending practices and IPs match authentication (DKIM, SPF, DMARC). Discrepancies lead to failures at stricter ISPs.
- Header Alignment: Ensure the 'header from' domain aligns with DKIM and SPF records. Misalignment can trigger DKIM failures and DMARC issues.
Key considerations
- Content Integrity: Minimize content alteration by using encryption and reducing intermediaries to preserve the DKIM signature.
- DNS Accuracy: Double-check all DNS configurations and use validation tools to ensure correctness and propagation.
- ISP-Specific Requirements: Be aware of and comply with stricter ISP policies, especially concerning key length and record validation.
- Testing: Regularly test DKIM configurations with multiple email clients and providers to identify and address issues early.
- Record Alignment: Ensure full alignment between DKIM, SPF, DMARC and sending domain to avoid authentication failures.
- Reputation: Maintain a good sender reputation and email practices to improve deliverability.
Marketer view
Email marketer from Return Path says to check if the sending practices and IPs match the authentication (DKIM, SPF, DMARC) of your emails. Discrepancies or inconsistencies might cause failures at certain ISPs with stricter policies.
19 Nov 2023 - Return Path
Marketer view
Email marketer from Stack Overflow shares that checking for common configuration errors, like incorrect selector names or typos in the DNS TXT record, is a key troubleshooting step. Provides tools to help with DKIM record validation to verify the correctness of the DNS settings.
22 Jul 2021 - Stack Overflow
What the experts say
6 expert opinions
DKIM failures at some ISPs but not others are primarily attributed to DNS-related issues. These issues include DNS misconfiguration, inconsistent DNS record propagation or caching by different ISPs, broken authoritative DNS servers, and problems with Azure DNS settings (like wildcard records). Incorrect DKIM setup, syntax errors in DNS records, and mismatches in DKIM selectors are also significant factors. Some ISPs might use outdated or cached DNS records, while others query DNS in real-time, leading to inconsistent DKIM authentication results. Factors such as inconsistencies in MIME formatting or header encoding, with some ISPs being sensitive to minor variations, and problems with the domain where the DKIM public key is located, also contribute to the problem.
Key opinions
- DNS Misconfiguration: Incorrect DNS settings are a primary cause of DKIM failures. This includes incorrect NS records, wildcard DNS entries, and misconfigured DNS servers.
- Inconsistent DNS Propagation/Caching: Different ISPs may use outdated DNS servers or have varying caching intervals, leading to discrepancies in DKIM record retrieval.
- Broken Authoritative DNS Servers: Intermittent failures can be caused by authoritative DNS servers that are not configured correctly.
- Incorrect DKIM Setup: Errors in DKIM setup, such as DNS record syntax errors or mismatches in DKIM selectors, contribute to failures.
- Encoding Errors: Some ISPs are sensitive to minor encoding errors, particularly in MIME formatting or header encoding.
- Public Key Location Issues: Problems with the domain where the DKIM public key is located can cause failures.
Key considerations
- Verify DNS Configuration: Ensure DNS records are correctly configured and propagated across all DNS servers.
- Utilize DNS Tools: Employ tools like XNND and DNS Viz to check DNS configuration and troubleshoot issues.
- Address Wildcard DNS Entries: Consider removing or adjusting wildcard DNS entries if they interfere with DKIM authentication.
- Correct DKIM Setup: Verify the DKIM key's correctness, DNS record syntax, and selector matches.
- Handle Encoding Issues: Ensure proper encoding (e.g., UTF-8) is used to avoid discrepancies between sending and receiving servers.
- Test with Multiple ISPs: Test DKIM authentication with various ISPs to identify specific issues and inconsistencies.
Expert view
Expert from Email Geeks notes Google has extensive data from 8.8.8.8, allowing them to identify which authoritative servers are not functioning correctly and potentially cache positive responses.
10 Oct 2022 - Email Geeks
Expert view
Expert from Email Geeks shares that intermittent DKIM failures seen by some ISPs are often due to only some DNS servers being configured correctly. Suggests it's likely a broken authoritative DNS server in this case since multiple ISPs are affected and to use testing to confirm.
18 Aug 2024 - Email Geeks
What the documentation says
4 technical articles
DKIM failures at some ISPs but not others can stem from several technical issues. These include DNS propagation problems where some ISPs use outdated records, character encoding inconsistencies leading to hashing mismatches, insufficient DKIM key lengths, and improper implementation of email signatures. Resolving these involves correctly configuring and propagating DNS records, standardizing character encoding (e.g., UTF-8), ensuring sufficient DKIM key length (e.g., 2048 bits), and properly generating and publishing the DKIM key.
Key findings
- DNS Propagation: DKIM failures may indicate DNS propagation issues, with some ISPs using outdated records.
- Character Encoding: Inconsistent character encoding can lead to hashing mismatches and DKIM failures.
- Key Length: Insufficient DKIM key length or lack of support by the receiving ISP can cause failures.
- Signature Implementation: Improper implementation of email signatures can lead to DKIM failures.
Key considerations
- Verify DNS Records: Ensure DNS records are correctly configured and propagated across all ISPs.
- Standardize Encoding: Standardize character encoding across all emails (e.g., using UTF-8).
- Ensure Sufficient Key Length: Use a DKIM key of sufficient length (e.g., 2048 bits) that is compatible with major ISPs.
- Properly Implement Signatures: Generate, publish, and configure email signatures correctly for proper DKIM implementation.
Technical article
Documentation from dmarcian details that inconsistent character encoding can cause DKIM failures. Different ISPs may handle character sets differently, leading to hashing mismatches. Standardizing character encoding (e.g., UTF-8) across all emails can mitigate this issue.
13 Jan 2023 - dmarcian
Technical article
Documentation from Google explains that DKIM failures at specific ISPs may indicate DNS propagation issues. Some ISPs might be using outdated DNS records, while others have updated records. Resolving requires ensuring DNS records are correctly configured and propagated.
11 Nov 2024 - Google
Do SPF and DKIM records need to be aligned for all email service providers?
How can I troubleshoot DMARC failures and identify the cause of authentication issues?
How do I fix DKIM alignment errors and configure DKIM signing for a custom domain in Microsoft 365 and is include:spf.mtasv.net required for mailchimp?
How do I properly set up SPF and DKIM records for email marketing, including handling multiple SPF records, IP ranges, bounce capturing, and Google Postmaster Tools verification?
How do I troubleshoot DMARC, SPF, and DKIM setup issues in Klaviyo?
What are SPF, DKIM, and DMARC, and when are they needed?
