Question 1

What is DKIM and how does it work?

Accepted Answer

DKIM (DomainKeys Identified Mail) is an email authentication method that uses cryptographic signatures to verify email authenticity. When sending emails, the mail server signs the message with a private key. Receiving servers use the public key published in DNS TXT records to verify the signature, ensuring the email hasn't been tampered with.

Question 2

Why is my DKIM validation failing?

Accepted Answer

DKIM validation can fail due to incorrect DNS records, mismatched selectors, expired keys, modified email content during transit, or configuration errors in the mail server. Check that the DKIM record exists in DNS, the selector matches, and the public key is correctly formatted. Email forwarding can also break DKIM signatures.

Question 3

What is a DKIM selector?

Accepted Answer

A DKIM selector is a string that identifies which DKIM key to use for verification. It's part of the DNS record name (selector._domainkey.domain.com) and allows domains to have multiple DKIM keys for different purposes or mail servers. Common selectors include dates, server names, or service identifiers like "google" or "mailgun".

Question 4

How often should I rotate DKIM keys?

Accepted Answer

Rotate DKIM keys every 6-12 months for security best practices. Some organizations rotate monthly or quarterly for high-security environments. When rotating, publish the new key first, update mail servers to use it, then remove the old key after ensuring all emails in transit have been processed.

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