Your files stay on your device # MTA-STS checker Check a domain's MTA-STS DNS record and HTTPS policy file, and whether the policy covers its real MX hosts. Press the button to run the check Nothing leaves this page until you do. The tool reads the DNS record, fetches the policy file at mta-sts./.well-known/mta-sts.txt, resolves the live MX hosts, and checks that the policy's patterns actually cover them. RFC 8461 has three halves and they all have to agree: the _mta-sts TXT record, the HTTPS policy file, and the MX list. This tool reads all three but opens no SMTP connection: it cannot check the TLS certificates your MX hosts present, and it does not model a sender's cached-policy behavior. A policy pattern may start with *. to match exactly one leading label; anything else is matched literally. Options ## More network tools - [Live DNS lookup](/network/dns) - [DNS explainer](/network/dns-explain) [All network tools](/network) Was this tool useful? YesNo --- Canonical HTML: https://nutter.tools/network/mta-sts-checker Markdown version: https://nutter.tools/network/mta-sts-checker.md Plain-text version: https://nutter.tools/network/mta-sts-checker.txt Agent index: https://nutter.tools/llms.txt