Exchange does not accept any email from POPcon. Error message: "530 5.7.0 Must  issue a STARTTLS command first"

POPcon needs to connect to the SMTP protocol in Exchange without authentication. This error indicates that Exchange was configured not to accept connections without authentication. You need to change the configuration like this:

You will find the settings for the SMTP server under Servers/Protocols/SMTP/Default SMTP Virtual Server. Open the properties by right-clicking on the Default SMTP Virtual Server and choosing "Properties":

The settings on tab "General" can normally be left to the defaults.

On the tab "Access" you can find some configuration settings that might interfere with POPcon.

POPcon only works with a standard SMTP connection WITHOUT authentication, so allow "Anonymous access" in the "Authentication" dialog: