What tools or scripts can fix common DKIM problems like formatting errors or length issues?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 May 2025
Updated 19 Aug 2025
7 min read
DKIM, or DomainKeys Identified Mail, is a critical email authentication standard that helps protect your email domain from spoofing and phishing attacks. It allows a recipient email server to verify that an email was authorized by the domain owner. However, setting up and maintaining DKIM records can sometimes lead to frustrating issues, particularly with formatting errors and length limitations.
Common problems often stem from the public key published in your domain's DNS as a TXT record. These can range from incorrect key lengths, misaligned values, or unintended characters that creep in during manual setup. When these issues occur, your emails might fail authentication checks, leading to them being flagged as spam or rejected entirely by recipient mail servers.
While there isn't a magical 'fix-all' script for every DKIM problem, there are numerous tools and practices that can help diagnose, prevent, and resolve common formatting and length issues. Understanding these resources is key to ensuring your emails consistently reach their intended inboxes.
Many DKIM problems originate from issues with the public key itself, which is published as a TXT record in your DNS. One of the most frequent challenges is the 255-character limit imposed on DNS TXT records. If your DKIM public key is longer than this, it must be split into multiple string parts, typically enclosed in double quotes. Incorrectly concatenating these parts, or failing to concatenate them at all, can lead to validation failures.
Formatting errors are also rampant. These can include extraneous spaces, missing or extra quotes, unintended line breaks, or special characters that corrupt the base64 encoded key. These seemingly small discrepancies can render your DKIM record invalid, preventing proper email authentication.
Understanding common record structures
A typical DKIM public key for a 1024-bit key usually starts with MIG and ends with QAB, while a 2048-bit key typically starts with MII and also ends with QAB. Understanding these initial characters can offer a quick visual check for your DKIM key length.
Multiple DKIM records for the same selector can also cause confusion and validation failures, even if each record is individually correct. This is why careful management of your DNS records is vital for successful email delivery.
In addition to simple formatting, the cryptographic aspects of DKIM, such as invalid RSA public key errors or issues leading to DKIM body hash failures, can complicate matters. These often require a deeper dive into how the DKIM signature is generated and applied by your sending system.
Tools for diagnosing DKIM issues
While there aren't scripts to automatically 'fix' a malformed DKIM record in your DNS, a variety of online tools can quickly diagnose issues. These tools are invaluable for pinpointing exactly what's wrong with your published DKIM public key.
Online DKIM checkers are typically the first line of defense. You input your domain and DKIM selector, and the tool performs a DNS lookup to retrieve your DKIM TXT record. It then checks the record for common syntax errors, proper concatenation, and the validity of the public key. Tools like DKIM Validator are excellent for this purpose.
Many of these checkers also verify the DKIM signature itself against a test email, which can help diagnose issues beyond simple DNS record problems, such as header canonicalization or body hash mismatches. They offer clear, actionable feedback on what needs to be corrected. Remember, our guide on troubleshooting DKIM failures provides more in-depth steps.
Beyond dedicated DKIM tools, general DNS lookup utilities also come in handy. These can confirm that your TXT record is correctly published and propagated across the internet. If a tool reports that no DKIM record was found, a basic DNS check is a good starting point.
Tool Type
Primary Function
Key Benefits
Online DKIM checkers
Validate TXT record syntax and public key format.
Provide immediate feedback on common errors, including concatenation issues.
DNS lookup tools
Confirm record publication and global propagation.
Help verify visibility of your DKIM records across DNS servers.
Email deliverability testers
Send test emails to analyze authentication results comprehensively.
Identify if DKIM is passing or failing from the recipient's perspective, like our email deliverability tester.
Preventing DKIM formatting and length issues
The most effective way to address DKIM formatting and length issues is to prevent them from happening in the first place. This often involves leveraging reliable DKIM record generators and adopting robust key management practices.
Many Email Service Providers (ESPs) and email platforms offer built-in DKIM record generation. When you configure DKIM for your domain through these platforms, they often provide you with the correctly formatted TXT record, automatically handling length concatenation and ensuring proper syntax. This significantly reduces the chance of human error during the copy-pasting process.
Manual DKIM setup
Higher risk: Prone to typos, extra spaces, or incorrect concatenation leading to formatting errors.
Length issues: Requires manual splitting of keys into 255-character segments, which can be error-prone.
Time consuming: More effort required for initial setup and troubleshooting.
For those managing their own email infrastructure or who need to generate keys independently, several tools are available to help generate DKIM public and private keys. These generators create the necessary key pairs and often provide the public key in the correct TXT record format, ready for direct pasting into your DNS settings. This dramatically reduces the likelihood of manual formatting mistakes.
Additionally, adhering to best practices like regular DKIM key rotation, as recommended by organizations like M3AAWG, and using clear DKIM selector naming conventions (e.g., including rotation dates in selectors) can help maintain an organized and error-free DKIM setup over time. This proactive approach minimizes the need for reactive fixes.
Addressing specific DKIM challenges
Some specific DKIM challenges, like cryptic base64 errors or issues related to quotation marks in the record, often point directly back to improper formatting. When troubleshooting, it's crucial to inspect the raw TXT record value precisely as it appears in your DNS.
For base64 errors, ensure that no non-base64 characters have inadvertently been introduced. This can happen with copy-pasting from text editors that automatically convert straight quotes to curly quotes or add invisible characters. Always use a plain text editor when working with DNS records.
If you're dealing with a DKIM record that fails to authenticate, it might also be helpful to consult our guide on decoding DKIM temperror messages. These temporary errors can sometimes mask underlying formatting or DNS propagation issues. Addressing these foundational problems is essential for achieving consistent DKIM pass rates and improving your email deliverability.
Ensuring robust email authentication
While there isn't an automated script to magically correct every DKIM formatting or length error in your DNS, the best solutions lie in a combination of powerful diagnostic tools and preventive best practices. Leveraging online validators and ensuring proper record generation from your ESP or a dedicated key generator will significantly reduce the occurrence of these common problems.
Consistent monitoring of your DKIM records and swift action on any reported authentication failures are crucial for maintaining strong email deliverability. By understanding the common pitfalls and utilizing the right tools, you can ensure your emails are consistently signed correctly and authenticated by recipient servers, improving your sender reputation and inbox placement.
Views from the trenches
Best practices
Always use a reputable email service provider's DKIM generation tools if available to avoid manual errors and ensure correct formatting.
Regularly validate your published DKIM records using online checkers to catch issues immediately after changes are made.
Implement a consistent key rotation schedule and use clear selector naming conventions for better organization.
Common pitfalls
Manually copying and pasting DKIM records without careful attention to hidden characters, spaces, or line breaks.
Exceeding the 255-character DNS TXT record limit without properly concatenating the key into multiple strings.
Having multiple DKIM records for the same selector, which can cause unpredictable authentication results.
Expert tips
Automate DKIM record deployment directly via API if your DNS provider and ESP support it, eliminating human error.
Use version control for your DNS configurations if possible, allowing for easy rollback of erroneous changes.
When troubleshooting, check the raw DNS TXT record for any non-standard characters introduced by text editors.
Expert view
Expert from Email Geeks says that common DKIM issues often stem from errors in the value portion of the published DKIM public key, and while there are no direct scripts to fix these, ongoing efforts focus on preventing them by automating the setup process to remove human intervention.
2024-11-06 - Email Geeks
Marketer view
Marketer from Email Geeks says that frequent DKIM problems include keys being too long, requiring minimum concatenation to stay within the 255-character limit, and other formatting errors, such as cryptic base64 errors, unintended line breaks, or special characters that need to be stripped out.
