What is a DKIM selector and how is it chosen?

A DKIM selector is a label that tells receiving mail servers exactly where to find the public key for verifying your email's signature. Every DKIM-signed email includes a selector name. Receivers use it to look up the matching key in your DNS and confirm the signature is valid.

You might have several DKIM keys published at once (one per sending service), and the selector is how receivers know which key to grab for any given message.

Where it lives in DNS

DKIM public keys are published at DNS records with this format:

selector._domainkey.yourdomain.com

So if your ESP uses a selector called "s1" on the domain deepcurrent.io, the key would live at:

s1._domainkey.deepcurrent.io

And every email signed by that key would carry s=s1 in the DKIM signature header so receivers know exactly which record to look up.

How selectors are chosen

And in In most cases, your ESP picks the selector name, not you. When you set up DKIM with Mailchimp, Klaviyo, Postmark, or any other sending platform, they'll give you a selector name and the public key to publish. You paste what they give you into DNS at the right subdomain. The name itself ("k1", "em1234", "s2") is just a label. It doesn't affect deliverability.

If you're running your own mail server, you choose the name when you generate the keypair. Pick something simple and descriptive ("2026-q1" is a popular pattern for rotation tracking).

Multiple selectors

If you use multiple sending services, each one gets its own selector. That's expected and normal. You can look up any selector published on your domain with our DKIM checker. If you're seeing DKIM fail in headers and you're not sure which selector is the problem, the email's Authentication-Results header will name it. The SOS hotline is free if you need help tracing it.