Find every subdomain
of a domain.

Every hostname under a domain that ever appeared in a public TLS certificate — with certificate counts, first/last seen and live DNS status.

5 hosts · 279 ms

HostCertsFirst seenLast seenDNS
mailsynth.com 19 2026-04-27 2026-09-24 ok
*.mailsynth.com 8 2026-05-28 2026-09-24 —
app.mailsynth.com 3 2026-05-17 2026-09-01 ok
investors.mailsynth.com 3 2026-05-23 2026-09-10 ok
www.mailsynth.com 13 2026-04-27 2026-08-24 ok

Programmatic access, with DNS A records: API GET /v1/hosts/mailsynth.com (API key for paging).

Shown here: hostnames with a certificate that is valid now or expired within the last 90 days. The full history since 2013 — hostnames whose last certificate expired earlier — is a Pro plan method: GET /v1/hosts-history/mailsynth.com.