DNS and Network troubleshooting and diagnostic tools integrated into one sweet interface.| mxtoolbox.com
SMTP MTA Strict Transport Security (MTA-STS) is a mechanism enabling mail service providers (SPs) to declare their ability to receive Transport Layer Security (TLS) secure SMTP connections and to specify whether sending SMTP servers should refuse to deliver to MX hosts that do not offer TLS with a trusted server certificate.| IETF Datatracker
There are reasons I run my own mail server, they may seem paranoid but they are not. Well. not too paranoid...| Mark Loveless