Are 2048-bit DKIM keys well accepted by ISPs?

Key findings

• Broad acceptance: 2048-bit DKIM keys are widely accepted by most Internet Service Providers (ISPs), including major players like Gmail, which actively encourages their use for enhanced encryption. For more details, see this article on DKIM key length.
• Enhanced security: Double the key length provides a much stronger cryptographic signature, offering superior protection against spoofing and tampering. This makes emails more trustworthy for recipients.
• Industry standard: 2048-bit keys are increasingly becoming the recommended standard, aligning with current best practices for email authentication.
• DNS considerations: The primary technical challenge lies in publishing the longer key within the DNS TXT record limit, often requiring the key to be split into multiple strings.

Key considerations

• DNS provider compatibility: Before migrating, confirm your DNS provider supports the necessary concatenation for 2048-bit DKIM records. Some older or lower-tier providers may have limitations. You can learn more about which key sizes ESPs support.
• Thorough testing: Always test the proper publication and validation of the 2048-bit key in DNS before fully deploying it for email sending to avoid deliverability issues. This is crucial for maintaining your domain reputation.
• Future-proofing: Adopting 2048-bit keys helps your email infrastructure stay current with evolving security standards and prepares for potential future requirements, as detailed in this Twilio article on key best practices.
• Complexity management: While 2048-bit keys offer better security, the increased length can introduce minor complexities in DNS record management that need careful attention.

Key opinions

• Near universal acceptance: Many marketers report that they haven't encountered any major ISPs that reject 2048-bit DKIM keys, indicating broad compatibility.
• Becoming standard: There's a growing sentiment among marketers that 2048-bit keys are evolving into a standard for email authentication, replacing older, less secure key lengths.
• High-profile usage: Marketers have successfully deployed 2048-bit keys for high-volume and high-profile clients for several years, demonstrating their effectiveness in demanding environments.
• Security benefits: The increased security offered by 2048-bit keys is seen as a significant advantage for protecting email streams from malicious activity.

Key considerations

• DNS record string limits: A common point of caution is that 2048-bit keys often exceed the character limit for a single DNS TXT record string, requiring the key to be split into multiple parts.
• DNS provider variations: Marketers note that different DNS providers handle the splitting and concatenation of multi-string TXT records in varied ways, which can be frustrating to configure. You can check how to identify your DKIM key length.
• Lower-tier DNS support: While major DNS providers like Route 53 generally support 2048-bit keys, some lower-tier providers might not, necessitating a check before migration.
• Pre-deployment validation: It's critical to ensure the key is correctly published and validated in DNS before sending live email to avoid issues. Consider the pros and cons of different DKIM key lengths.

Key opinions

• Universal support expected: Experts largely expect 2048-bit DKIM keys to be supported by virtually every ISP, indicating widespread compatibility for senders. This broad acceptance facilitates a smoother transition for those upgrading their security protocols.
• Gmail's recommendation: Gmail has been recommending 2048-bit keys for some time, driven by its strong preference for encryption and enhanced security in email communications. This strong endorsement from a major ISP influences industry trends.
• Decreasing DNS issues: While DNS-related challenges for 2048-bit keys were once more prevalent, experts note that these issues are becoming less common, signifying improvements in DNS provider capabilities. More information is available in our discussion on new authentication requirements.
• Crucial testing: Regardless of improving DNS support, experts strongly advise testing the key's correct publication in DNS before its live use. This proactive step helps prevent potential deliverability disruptions and authentication failures. For more on this, read our guide to DMARC, SPF, and DKIM.

Key considerations

• Verify DNS publication: Even with improved support, always manually verify that the 2048-bit DKIM key is correctly entered and resolved in your DNS records. Incorrect entries can lead to validation failures.
• Leverage DMARC reports: Utilize DMARC reports to monitor how recipient servers are authenticating emails with the new 2048-bit key. These reports provide invaluable feedback for troubleshooting.
• Stay updated: Keep abreast of evolving best practices and any specific recommendations from major ISPs regarding DKIM key lengths and other authentication protocols. The landscape of email security is dynamic.
• Consistency across domains: For organizations managing multiple sending domains, ensure consistent application and testing of 2048-bit keys across all properties for uniform security posture.

Key findings

• Superior cryptographic strength: Documentation confirms that 2048-bit keys provide a higher level of security, making them more resilient against compromise than 1024-bit keys.
• RFC compliance: The DKIM standard (RFC 6376) supports varying key lengths, and larger keys are directly correlated with stronger signatures, aligning with the principles of secure email authentication.
• DNS TXT record constraints: A recurring theme in documentation is the necessity to manage the character limits of DNS TXT records, which often means splitting 2048-bit keys across multiple strings.
• Recommended best practice: Many technical guides and industry bodies now recommend 2048-bit as the current standard for robust and future-proof email authentication.

Key considerations

• DNS parsing behavior: It's crucial to understand how your specific DNS provider parses and concatenates multiple strings within a single TXT record to ensure correct key resolution.
• Strict adherence to specs: Ensure that your key generation and publishing processes strictly adhere to DKIM specifications to avoid validation errors, particularly for longer keys. Read more about RFC 6376.
• Validation tools utilization: Documentation often advises using DNS lookup and DKIM validation tools to confirm the proper publication and format of the 2048-bit key. You can check our recommended DKIM key lengths.
• Migration planning: Comprehensive planning for the migration process is essential, especially when dealing with the intricacies of DNS updates and ensuring no interruption to email flow.