How to quickly identify DKIM key length (1024 or 2048)?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 Jun 2025
Updated 17 Aug 2025
7 min read
Understanding the cryptographic strength of your DKIM (DomainKeys Identified Mail) keys is essential for maintaining email security and deliverability. DKIM uses a pair of cryptographic keys, a private key for signing outbound emails and a public key published in your DNS (Domain Name System) records, allowing receiving mail servers to verify the authenticity of your messages. The length of this key, typically 1024-bit or 2048-bit, directly impacts the security of your email authentication.
Identifying whether your DKIM key is 1024-bit or 2048-bit helps ensure compliance with current security best practices and prepares your domain for future email authentication requirements. While 1024-bit keys are still widely supported, the industry trend is moving towards stronger 2048-bit keys for enhanced security. Knowing your key length is the first step in assessing your domain's email security posture.
A DKIM record is a TXT record in your domain's DNS that contains the public key. This record is crucial because it allows recipient mail servers to fetch your public key and verify the digital signature on incoming emails. Without a correctly published DKIM record, your emails cannot be authenticated via DKIM, potentially leading to deliverability issues.
The public key itself is stored within the 'p=' tag of your DKIM TXT record. When you look up your DKIM record using a DNS lookup tool, you'll see a long string of characters following p=. This string is the public key. The length of this encoded string provides a strong indicator of whether it's a 1024-bit or 2048-bit key. You can also explore recommended DKIM key sizes for more context.
The choice of key length has significant implications for both security and compatibility. While 1024-bit keys offer a basic level of security, 2048-bit keys provide a much stronger cryptographic defense against potential attacks, making them the preferred choice for many organizations. It's important to understand the pros and cons of different key lengths to make an informed decision for your email infrastructure.
The simplest way to get a quick estimate of your DKIM key length is by visually inspecting the 'p=' value within your DNS TXT record. While not definitive, it offers a strong hint. A 1024-bit key will result in a shorter string of characters compared to a 2048-bit key. This method is often enough for an initial assessment before diving into more technical checks.
Generally, a 1024-bit key's public value (the string after 'p=') will be around 160-200 characters long, while a 2048-bit key will be significantly longer, often exceeding 300 characters. For a more precise understanding of character counts, you can refer to discussions like the one on Y Combinator's Hacker News, where users share their observations on key lengths based on the encoded string.
It's worth noting that some DNS providers have limitations on the length of TXT records, which can sometimes impact the ability to publish longer 2048-bit keys without splitting the record. If you encounter issues, understanding what causes DKIM key issues with DNS provider limits is crucial. This can affect your choice of key length or how you implement it.
1024-bit key characteristics
Typically, the 'p=' value is around 160-200 characters long. This shorter length is easier to copy and paste into DNS records.
Compatibility: Generally well-accepted by most older and current mail systems.
Security: Considered less secure than 2048-bit keys due to advancements in computational power.
2048-bit key characteristics
The 'p=' value is significantly longer, often over 300 characters. This may require splitting the TXT record in some DNS management interfaces.
Compatibility: Increasingly preferred by major mailbox providers like Google and Yahoo.
Security: Offers a higher level of cryptographic strength, better resisting brute-force attacks.
Automated tools and commands for verification
For a definitive answer on your DKIM key length, you'll need to use specific tools or command-line utilities. These methods analyze the public key directly from your DNS record, providing an accurate cryptographic assessment rather than a visual estimate. Using these tools helps troubleshoot DKIM failures related to key configuration.
Several online DKIM key checkers can retrieve your DKIM record and report its key length. Tools like the Protodave DKIM Key Checker are user-friendly, requiring only your domain and DKIM selector to provide a detailed analysis, including key length. These are excellent for quick checks without needing technical expertise.
For command-line users, you can first retrieve the DKIM TXT record using dig or nslookup, then extract the 'p=' value. Once you have the public key string, you can use the openssl command to decode it and determine its length. This provides the most accurate and verifiable method for identification.
To use this, save your DKIM public key (the string after 'p=', enclosed within `-----BEGIN PUBLIC KEY-----` and `-----END PUBLIC KEY-----` tags) into a temporary file, for example, named DKTEMP. The output of the openssl command will include the key length in bits, confirming whether it's 1024, 2048, or another size. This is the most reliable way to know your exact key strength.
Why verifying your DKIM key length is crucial
Regularly verifying your DKIM key length is more than just a technical exercise, it's a critical component of your overall email security and deliverability strategy. Stronger keys, like 2048-bit ones, offer greater protection against cryptographic attacks that could otherwise allow malicious actors to forge emails from your domain, harming your brand reputation and potentially leading to your domain or IP being added to a blacklist (or blocklist).
Furthermore, major mailbox providers are increasingly favoring or even requiring stronger authentication standards, including longer DKIM keys. Staying ahead of these changes, such as the potential for 2048-bit DKIM keys becoming new requirements, can significantly improve your inbox placement rates and ensure your legitimate emails reach their intended recipients. This also ties into the recommendation for DKIM key rotation for security.
Best practice for DKIM key length
While 1024-bit DKIM keys are still functional, the consensus among security and email deliverability experts is that 2048-bit keys provide superior protection. Upgrading to a 2048-bit key is a proactive step to enhance your domain's security and maintain optimal email deliverability in an evolving threat landscape.
Views from the trenches
Best practices
Actively use automated tools to routinely check and confirm your DKIM key length, ensuring cryptographic strength.
Consider upgrading to a 2048-bit DKIM key to align with current security standards and improve email deliverability.
Regularly monitor your DKIM records for proper configuration and prevent any issues that might affect validation.
Always consult your DNS provider's documentation regarding TXT record length limitations before publishing new DKIM keys.
Common pitfalls
Relying solely on visual inspection to determine key length, which can lead to misidentification and security vulnerabilities.
Ignoring DNS provider TXT record limits, which can cause truncation or rejection of longer 2048-bit DKIM keys.
Failing to update DKIM keys to stronger lengths as security standards evolve, leaving your domain vulnerable.
Not testing DKIM authentication after making changes to your DNS records, leading to unexpected delivery issues.
Expert tips
Developing simple scripts for common tasks like DKIM key analysis can significantly streamline your email deliverability efforts.
Leveraging online tools that check DKIM key length is a quick and effective way to monitor your authentication setup.
Using command-line tools like OpenSSL offers a precise and verifiable method to confirm the exact cryptographic strength of your DKIM keys.
Staying informed about the latest email authentication requirements and proactively adapting your configurations is crucial for inbox placement.
Expert view
Expert from Email Geeks says they developed a Python script for automated DKIM key length identification.
2024-11-06 - Email Geeks
Marketer view
Marketer from Email Geeks says that online tools like Wombatmail can provide key length information.
2024-11-06 - Email Geeks
Securing your email with proper DKIM key management
Identifying your DKIM key length, whether 1024-bit or 2048-bit, is a crucial step in maintaining robust email authentication. While a quick glance at the public key's character count can offer a hint, precise verification is best achieved using dedicated online tools or command-line utilities like openssl. These methods ensure you have accurate information about your cryptographic strength.
As email security standards continue to evolve, moving towards stronger cryptographic keys like 2048-bit is becoming increasingly important for optimal deliverability and protection against spoofing. Regularly assessing and upgrading your DKIM setup will help ensure your emails remain authenticated and trusted by receiving mail servers.
Google and 
Yahoo.
