All I had to do was disable the "SMTP Proxy" under "Security", "Proxy settings" in the server-manager, then make sure my local users were configured to use a valid off-site SMTP server.
SMTPSmartHost is set under "Configuration", "E-mail", "Address of Internet provider's mail server" in server-manager -- but would only be relevant if you were using your SME box as a mail server or SMTP proxy.