Glossary
DKIM selector
The `s=` value in a DKIM signature that subdivides a signing domain's key namespace, so one domain can publish and use several public keys at the same time.
In plain terms
A label that says which of your published keys signed this particular message.
Why it matters for deliverability
Selectors are what make key rotation possible without downtime, and what let several providers sign for the same domain simultaneously without colliding.
What to do about it
- Give each sending provider its own selector.
- Rotate by publishing a new selector, switching signing to it, then removing the old one.
- Never reuse a selector name across providers.
Source
RFC 6376 — DomainKeys Identified Mail (DKIM) Signatures
“To support multiple concurrent public keys per signing domain, the key namespace is subdivided using "selectors".”
Checked 2026-08-29
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