@pbarney Cool it, please. @just4t is trying to help. Mail-in-a-Box is not normally meant to be a SMTP relay and this forum isn’t for asking for basic system administration help.
To use Mail-in-a-Box as an SMTP relay, you’ll need to configure your server to connect in the same way a mail app would — the documentation for that is in your box’s Mail-in-a-Box control panel. We also have some notes at https://mailinabox.email/advanced-configuration.html.