Glossary
DKIM Selector — What It Is and How It Works
A DKIM selector is a string that identifies which DKIM public key to use when verifying an email's signature. It appears in the DKIM-Signature header as s=[selector] and must match a DNS TXT record published at [selector]._domainkey.yourdomain.com. Selectors allow a domain to have multiple DKIM keys — useful when using different sending providers or rotating keys.
Common Selectors by Provider
- google — Google Workspace
- selector1, selector2 — Microsoft 365
- s1, s2 — SendGrid
- k1 — Mailgun
- pm — Postmark
- default, mail, dkim — common generic names
How to Find Your Selector
Check the DKIM-Signature header in a raw email. The s= tag shows which selector was used.
Probe DKIM DNS in DNS Preflight
Open DNS Preflight →FAQ
What is a DKIM selector?
A label that identifies which DKIM public key to use for verification. It appears in the DKIM-Signature header and must match a DNS TXT record.
Can I have multiple DKIM selectors?
Yes — each selector is independent. Multiple selectors are used when you have different sending providers or during key rotation.
How do I find which selector my emails use?
Check the raw email headers — look for DKIM-Signature: s=[selector].