SMTP MTA-STS is a work in progress and this tool is provided to assist domain owners in publishing a policy. We examine the following locations:
The tool currently does not evaluate IETF draft-00 or draft-01 versions of the spec so policies at _mta_sts.example.com or with v=STS1 are considered invalid.
Checking draft 2 & 3 policies. Draft 3 support added March 31, 2017.