How should DKIM selector names be interpreted and what is the recommended DKIM key size?
Summary
What email marketers say11Marketer opinions
Email marketer from MXToolbox suggests that DKIM selectors should be short, alphanumeric strings. They also mention that selectors should be unique to prevent conflicts when using multiple DKIM keys.
Email marketer from Reddit (u/EmailExpert) shares that while 2048-bit keys are generally recommended, some older systems might have issues with keys larger than 1024 bits. It's essential to test compatibility.
Email marketer from mailhardener.com specifies that the recommended DKIM key size as of today, should be 2048-bit. If for some reason you can't, then 1024 bits is acceptable, however, anything below that is unsafe and should be avoided.
Marketer from Email Geeks answers that if a DKIM selector is "201802", it would be interpreted as the key not being rotated since 2018.
Email marketer from StackOverflow (TechGuru) explains that DKIM selectors can be named using a convention that includes the year and quarter in which the key was generated to help with tracking and rotation, but it's not a strict requirement.
Email marketer from SendGrid shares that while 1024 bit keys are supported, 2048 bit keys should be implemented because they offer significantly more protection against spoofing and are less likely to be compromised.
Marketer from Email Geeks remembers doing a project to move to 2048-bit keys in 2017-2018 and believes the RFC allowing 4096-bit keys was released in 2018.
Email marketer from SparkPost suggests that DKIM selectors should be descriptive and indicate the purpose or generation date of the key. This helps with key management and troubleshooting.
Marketer from Email Geeks says that a minimum DKIM key size now is 2048, 4096 should be a goal.
Email marketer from easydmarc.com mentions the standard DKIM key size is 2048-bit as a minimum. It protects against vulnerabilities and provides the best level of security.
Email marketer from dmarc.org recommends using a key length of 2048 bits or greater to ensure adequate security and compatibility with modern email systems.
What the experts say2Expert opinions
Expert from Spamresource mentions that the selector is arbitrary and is used to publish multiple public keys. They also suggest to check the RFC for more specific information on syntax.
Expert from Email Geeks bumped his keys to 2048 and rotates them after 2-5 years.
What the documentation says4Technical articles
Documentation from Google Workspace Admin Help recommends regularly rotating DKIM keys. Using a new selector for each key rotation improves security by limiting the impact of a compromised key.
Documentation from Cloudflare.com states that a DKIM selector is a string that identifies the DKIM key pair used to sign an email. It tells the receiving server where to look up the public key to verify the signature.
Documentation from Valimail.com explains that DKIM selectors are used to facilitate key rotation and management. Selectors allow senders to publish multiple DKIM keys and receivers to determine which key to use for verification.
Documentation from datatracker.ietf.org (RFC 8301) specifies that RSA keys used for DKIM signatures MUST be at least 1024 bits long and SHOULD be 2048 bits or longer. It also discusses the implications of key size on security and performance.