Actually, you put it into the Pickup directory and smtp will move it into the Queue. I use it frequently just to check it SMTP is installed properly.
A couple of minutes after it disappears from Pickup, you then check the other directories under mailroot for any newly created files. If everything went well, there'll be none.
If there are some, you can open them with a text editor. One common message can be something like "Delivery Delayed or Delivery Stopped". Usually means you need to set permissions to allow it through your firewall/proxy/Anti-Virus stuff.
You can also see some types of messages because some ISP's require that you authenticate with them before they pass along any port 25 traffic. In that instance, you'd set the smtp outbound properties to Basic Authentication.