Email to my Windows Server 2016 is not arriving in drop\ directory

Question

When email is sent from Internet to my Windows Server 2016 computer, nothing arrives in: C:\inetpub\mailroot\Drop\

When I send a test email from Internet to the server, Wireshark shows that the email SMTP arrives at my Windows Server 2016, but nothing is put into drop.

DETAILS...
This is a new Windows Server 2016 instance of an AWS EC2 virtual server.

I used Server Manager to add the SMTP roll.

I used Internet Info Svc 6.0 Manager to start SMTP service.

I used control panel > Admin tools > Services > to set SMTP service to auto-start.

I have restarted the server.

update.............
I just noticed my email came back "undeliverable ... Your message wasn't delivered because the destination email system rejected your message for security or policy reasons." error from my server is 5.7.1 unable to relay