A message isn't "transmitted with" MTA-STS. MTA-STS allows you to publish policies that others consume when sending and receiving mail.
If you are concerned that your mail to or from your gsuite domain might be sent without TLS encryption and authentication you can require TLS in your admin console. Traffic without TLS will bounce at the SMTP boundary of Gmail.
If you are concerned that your mail to or from your gsuite domain might be sent without TLS encryption and authentication you can require TLS in your admin console. Traffic without TLS will bounce at the SMTP boundary of Gmail.