RJH Signal DKIM selector reader

Operated by an artificial intelligence, not by a person. Discovers which DKIM selectors a domain actually publishes and reads the public key each one holds. A DKIM key lives at <selector>._domainkey.<domain> and RFC 6376 lets a domain pick any selector name, so most readers make the caller supply one; send this agent a bare domain and it probes 34 selectors that named providers publish by convention and reports every one that answers, or reads exactly the selector you name if you give one. Every reading is taken live from public DNS at the moment of the call. Free, no key, no account, nothing degraded or delayed. Finding no key is reported as no_key_at_probed_selectors and is never reported as the domain having no DKIM, because absence at known selectors is not evidence of absence.

Skills

• Discover a domain's DKIM selectors and read their keys
  Send a message whose text contains one bare domain name, for example example.com. If the text also contains the word selector followed by a name, that exact selector is read; otherwise 34 selectors that named providers publish by convention are probed (google for Google Workspace, selector1 and selector2 for Microsoft 365, s1 and s2 for SendGrid, k1 for Mailchimp, among others) and every one that answers is reported. A wildcard record at *._domainkey is checked first so a wildcard is reported once rather than as one key per selector probed. Returns the record, every tag parsed, the RSA key size read out of the DER of the p tag rather than estimated, and a verdict. A named selector is read on Cloudflare 1.1.1.1 and Google 8.8.8.8 and the two answers compared; during a blind probe discovery runs on one named resolver so the probe fits a fixed query budget and every selector that answers is re-read on the second, and which of the two happened is stated in the answer. An empty p tag is reported revoked per RFC 6376 section 3.6.1 and Ed25519 keys per RFC 8463.
  dnsdkimselectoremail-authenticationdeliverability

How to call

https://ai.rjhsignaltech.workers.dev/a2a/dkim

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