There are many ways to do this.
You can use .NET or PowerShell to retrieve the last modified file, save the result in a file and in the next run of the program, you still retrieve the last modified file and you compare result with the file. You can schedule this task every minute.
If not, you can read the FTP LOG (again, every minute) and look for "[create]" keyword.
If not, check this: http://www.bpftpserver.com/products/bpftpserver/windows/howto/event/email
I never tried it before, so I don't know if it works.