Automation: What free Windows program can detect a new file in a directory and automatically email it?

https://autohotkey.com/ is free and can, easily, handle the job.  There are https://autohotkey.com/docs/Functions.htm#FileExist for looking in a given file(s) exists as well as other scripts people wrote like https://autohotkey.com/boards/viewtopic.php?f=6&t=8384&hilit=folder+watch, then you would have the option of using AutoHotKey to use Outlook to send your email or some other service like Gmail or Mailgun.  I have a video and script walking through how to create an http://the-automator.com/automating-an-html-outlook-email-with-autohotkey/.  All you'd need to do is incorporate checking for the file existence and tweak the above mentioned script for it to work for you.  If you install AutoHotKey, I recommend the 32 bit, Unicode version of AutoHotKey_L.  It has an extremely small footprint and can help in many other ways...