DKIM s= tag
The required tag in a DKIM signature that names the selector, telling the verifier where under the d= domain to fetch the public key.
What it means
The verifier builds the key's DNS name from two tags: s= followed by _domainkey and the d= domain. s=mail2026 with d=example.com means the key lives at mail2026._domainkey.example.com.
Reading s= is the quickest way to find a domain's DKIM key when you do not know the selector, since DNS offers no way to list selectors. Open a signed message, read the DKIM-Signature header, and look up that name. If the lookup returns nothing, the signer is using a key the domain has not published (or has removed), and DKIM fails with no key.
The same letter appears in DKIM key records with another meaning, the service type, normally absent or set to email.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
All 432 terms in the glossaryThe wiki: blocklists and bounce codes