What is a DKIM selector?
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When the receiving server checks your DKIM signature, it needs to find your public key in DNS. The selector is how it knows where to look.
A DKIM selector is a short label that, combined with your domain, points to the DNS location of your DKIM public key. The DNS lookup format is: selector._domainkey.yourdomain.com.
So if your selector is s1, the receiving server looks up s1._domainkey.yourdomain.com to find your public key TXT record.
Selectors matter for a few practical reasons:
Multiple ESPs. If you're sending through two different ESPs, each one typically has its own selector. You can publish multiple DKIM keys under different selectors simultaneously. One might be mailchimp, another brevo. The signature on each email identifies which selector was used to sign it, and the receiving server looks up that specific one.
Key rotation. When you rotate your DKIM keys (which is good practice), you publish the new public key under a new selector, update your sending server to sign with the new private key, and then remove the old selector's DNS record after confirming the transition worked. That way you're never leaving a gap in verification during the switchover.
Your selector is typically chosen by your ESP during setup. They'll give you the exact DNS record to publish, which will include the selector name as part of the subdomain. You don't usually need to decide on a selector yourself unless you're running your own mail infrastructure.
If you want to look up your current DKIM record and confirm it's publishing correctly, our free DKIM checker will look up any selector you specify. You can also check how DKIM signing works to understand how the selector fits into the full verification process, or see why you might want multiple keys at once.
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