Result Type,Description,Reference
starttls-not-supported,This indicates that the recipient MX did not support STARTTLS.,[RFC8460]
certificate-host-mismatch,"This indicates that the certificate presented did not adhere to the
        constraints specified in the MTA-STS or DANE policy, e.g., if the MX hostname does not match any identities listed in the subject alternative name (SAN)
        [RFC5280].",[RFC8460]
certificate-expired,This indicates that the certificate has expired.,[RFC8460]
tlsa-invalid,"This indicates a validation error in the TLSA record associated
        with a DANE policy. None of the records in the RRset were found to be valid.",[RFC8460]
dnssec-invalid,This indicates that no valid records were returned from the recursive resolver.,[RFC8460]
dane-required,"This indicates that the sending system is
        configured to require DANE TLSA records for all the MX hosts of
        the destination domain, but no DNSSEC-validated TLSA records were
        present for the MX host that is the subject of the report. Mandatory DANE for SMTP is described in Section 6 of [RFC7672].
        Such policies may be created by mutual agreement between two
        organizations that frequently exchange sensitive content via email.",[RFC8460]
certificate-not-trusted,"This is a label that covers multiple
        certificate-related failures that include, but are not limited to,
        errors such as untrusted/unknown certification authorities (CAs),
        certificate name constraints, certificate chain errors, etc. When
        using this declaration, the reporting MTA SHOULD utilize the
        ""failure-reason-code"" to provide more information to the receiving entity.",[RFC8460]
sts-policy-invalid,This indicates a validation error for the overall MTA-STS Policy.,[RFC8460]
sts-webpki-invalid,"This indicates that the MTA-STS Policy could
        not be authenticated using PKIX validation.",[RFC8460]
validation-failure,"This indicates a general failure for a
        reason not matching a category above. When using this
        declaration, the reporting MTA SHOULD utilize the ""failure-reason-code""
        to provide more information to the receiving entity.",[RFC8460]
sts-policy-fetch-error,"This indicates a failure to retrieve an
        MTA-STS policy, for example, because the policy host is unreachable.",[RFC8460]