These instructions are necessary (see attached PDF below) if the email provider does not allow anonymous relaying, thus requiring Authentication (username & password).

Important: This guide shows how to install Internet Information Services (IIS) on a Windows computer (cannot be running a Windows Home Edition operating system). The computer must always be on during business hours.

Path where emails end up on Windows SMTP servers:  
C:\Inetpub\mailroot\Queue
C:\Inetpub\mailroot\Badmail 
 

Some SMTP servers like GMAIL require SSL in addition to authentication. Follow this guide (see PDF attachment) if your SMTP server requires SSL.