Summary
When DNS providers impose TXT record length limits, DKIM key issues arise, leading to authentication failures, deliverability problems, and potential spoofing. This can stem from truncated records or incorrect DMARC configurations. TXT records have a defined size limit, often 255 characters per string, and deviations from this standard or using duplicate TXT records cause issues. While concatenating strings within a TXT record or splitting keys into multiple records are potential workarounds, they aren't universally reliable. Competent DNS hosting is vital, and upgrading to providers supporting longer records is often the best solution. Verify complete DKIM keys with external tools and consider hacking client-side validations where applicable, while adhering to DNS record limits and ensuring the DNS system is RFC compliant.
Key findings
- TXT Length Limit: DNS providers' TXT record length limits (often 255 characters) can cause truncated DKIM keys.
- DKIM Authentication Failure: Incomplete DKIM keys lead to authentication failures, impacting email deliverability and security.
- UI Limitations vs System: DNS provider UI limitations might not accurately reflect the underlying DNS system's capabilities.
- Workaround Unreliability: Splitting long DKIM keys into multiple TXT records is not universally supported and may cause issues.
- Need for Competent DNS: Reliable DNS hosting from a competent provider ensures system stability and correct DMARC implementation.
- DMARC Configuration: Incorrect DMARC configurations and exceeding TXT record limits can impact email delivery.
Key considerations
- Verify Key Completeness: Use external tools and examine raw DNS records to ensure the DKIM key is complete and un-truncated.
- DNS Compliancy: Ensure that your host or registrar is RFC compliant.
- Strategic DNS Provider Choice: Consider upgrading to a premium DNS service or migrating to a provider that supports longer TXT records.
- Hacking Client-Side Validation: Javascript validations might bypass character limits.
- DNS System Security: Remember DNS is used to prove identity and stop malicious attacks.
What email marketers say
11 marketer opinions
When DNS providers impose TXT record length limits, DKIM key issues arise, causing authentication failures and deliverability problems. Several workarounds exist, including splitting the DKIM key into multiple TXT records or hacking client-side validations, but these are not universally reliable. Checking the raw DNS records and validating with external tools is recommended. Upgrading to a premium DNS service or migrating to a more compliant provider with better support for longer records and DKIM management is often the best long-term solution.
Key opinions
- TXT Limit Impact: TXT record length limits imposed by DNS providers can lead to incomplete or truncated DKIM keys.
- Authentication Failure: Incomplete DKIM keys cause DKIM authentication failures, impacting email deliverability.
- UI vs. Actual Limit: DNS providers may have UI limitations that don't reflect the actual DNS system's capabilities.
- Compliance Concerns: Many providers don't comply to a minimum of 255 character limit with TXT records.
Key considerations
- Verify Complete Key: Check the raw DNS records and validate DKIM keys with external tools to ensure completeness.
- Alternative Solutions: Consider splitting DKIM keys across multiple TXT records, recognizing potential compatibility issues.
- Migration to Compliant Provider: Evaluate upgrading to a premium DNS service or migrating to a more compliant provider that supports longer records and DKIM management.
- Javascript Validation: Client side character limits can often be bypassed with use of javascript validation.
Marketer view
Email marketer from SuperUser responds that some DNS providers have UI limitations that impose character limits even when the underlying DNS system supports longer records. They suggest checking the raw DNS records to confirm whether the entire key is actually being stored.
23 Jul 2021 - SuperUser
Marketer view
Email marketer from Email Geeks shares that sometimes those character limits are set up and enforced client side only, suggesting to try hacking the HTML or JavaScript validation.
17 Mar 2025 - Email Geeks
What the experts say
5 expert opinions
When DNS providers impose TXT record length limits, several issues arise impacting DKIM and DMARC. Duplicate TXT entries can invalidate DKIM keys. While multiple strings can be concatenated within a single TXT record, many providers have arbitrary limitations. Utilizing a competent DNS host is crucial for system stability. The Domain Name System (DNS) and TXT records are fundamental for email security and preventing malicious activity. Problems with DMARC setup, including incorrect or excessive TXT records, need proper attention and adherence to DNS record limits.
Key opinions
- Invalid DKIM Keys: Duplicate TXT entries will lead to an invalid DKIM key, resulting in failed DKIM signatures.
- TXT Record Concatenation: TXT records can contain multiple strings which are concatenated, allowing for larger records, but are often limited.
- Importance of Competent DNS: A competent DNS host is crucial for email system stability due to DNS impacts on DMARC records.
- DNS Security: DNS is fundamental in email and can be used by proving identitiy using TXT records, helping to prevent against malicious activity.
Key considerations
- DNS System Stability: Invest in a competent DNS host to ensure system stability.
- DMARC Setup: Pay close attention to DMARC configuration and ensure correct and appropriate TXT record usage.
- Avoid Duplicate Entries: Avoid duplicate TXT entries to maintain valid DKIM signatures.
- TXT Length Limits: Adhere to any DNS record limits as defined by the provider.
Expert view
Expert from Email Geeks explains that duplicate TXT entries will lead to an invalid DKIM key, and hence to no valid DKIM signatures.
9 May 2022 - Email Geeks
Expert view
Expert from Word to the Wise explains that because TXT records can be used to setup DMARC, problems can occur if there are too many of them, or they are not set up correctly. Advice is given to make sure any DNS record is not only correct but also conforms to any DNS record limits the provider might have.
22 May 2024 - Word to the Wise
What the documentation says
4 technical articles
TXT records have a defined size limit, commonly 255 characters per string, as per RFC standards. DNS providers that truncate DKIM records exceeding this limit can cause DKIM validation failures. When TXT record data exceeds the limit, it should be split into multiple strings within the same record for concatenation by the DNS resolver. Splitting the record is sometimes necessary for providers with length restrictions, however it is best practice to choose DNS providers that support longer records.
Key findings
- TXT Record Size Limit: TXT records commonly have a size limit of 255 characters per string.
- DKIM Record Truncation: DNS providers may truncate DKIM records exceeding the TXT size limit, leading to DKIM validation failures.
- String Concatenation: TXT data exceeding the limit should be split into multiple strings within the same record, concatenated by the DNS resolver.
- RFC Standard: TXT records must consist of one or more strings with a maximum length of 255 octets, as per RFC standards.
Key considerations
- Splitting Records: If splitting the record, implement correctly as per instructions to prevent DKIM failures.
- DNS Provider Choice: Opt for DNS providers that support longer records and avoid truncation to streamline DKIM configuration.
- DNS Compatibility: Ensure DNS records are compatible with existing DNS configurations.
Technical article
Documentation from RFC Editor details the standard format for TXT records, indicating that they consist of one or more character strings, each with a maximum length of 255 octets. DNS servers should support this standard, and deviations can cause interoperability problems.
27 Nov 2024 - RFC Editor
Technical article
Documentation from Google explains the process of adding a DKIM record to your domain's DNS records. If the DNS provider limits the TXT record length, splitting the record might be necessary, but providers supporting longer records are preferred.
4 Sep 2023 - Google
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