DKIM Selector (DKIM Selector)
Why You Should Care About DKIM Selector
Selectors allow a domain to use multiple DKIM keys simultaneously, which is essential when you use multiple email services. Google Workspace might use selector google, SendGrid might use selector s1, and your marketing platform might use selector mktg. Each service signs with its own private key and specifies its selector in the DKIM-Signature header so receivers know which public key to verify against.
Selectors also enable key rotation without downtime. You can publish a new key under a new selector, configure your email server to sign with the new key, and then remove the old selector's DNS record after a transition period. This prevents verification failures during the switchover.
When setting up DKIM, your email provider tells you the selector name and the corresponding DNS record to publish. If you change providers, you need to add the new provider's selector and remove the old one. Dangling DKIM records for decommissioned services do not cause delivery problems but should be cleaned up.
Checking Your Setup
A DNS health checker queries DKIM selectors for common email providers associated with your domain. You can also test specific selectors by looking up selector._domainkey.yourdomain.com as a TXT record.