MTA-STS API
Inspect a domain's SMTP transport-security posture — whether mail servers are required to deliver inbound mail over authenticated TLS, protecting it from downgrade and man-in-the-middle attacks. Pass a domain and the service fetches the MTA-STS policy file from mta-sts.<domain>/.well-known/mta-sts.txt (its version, mode, the permitted MX hosts and max_age), the _mta-sts DNS TXT record (its policy id) and the _smtp._tls TLS-RPT record (the rua reporting address), then reports whether MTA-STS is actually enforced and a prioritised list of issues — no policy file, no DNS record, a mode of only "testing", or a missing TLS-RPT record. A second endpoint returns just the parsed policy file. The request is made server-side and private/internal targets are refused (SSRF-guarded). Built for email-deliverability and anti-downgrade-attack audits, vendor and third-party assessment, and compliance. An MTA-STS / TLS-RPT checker — the SMTP transport-security counterpart to the email-authentication analyzer (emailsec, which covers SPF, DKIM and DMARC), and distinct from raw DNS lookup (dns). No upstream key, no cache.
api.oanor.com/mtasts-api
