This is a common problem when you need more secure connection. Microsoft explains the features of their FTP server here:
It is good to know that current FTP Service in IIS doesn't support Secure Sockets Layers (SSL). Of course that means your connection details and credentials to such service can be caught by Network listeners between you and the server. Therefore if you need secured connection you have to consider usage of Webdav over SSL or another FTP server which supports SSL.
A suggestion for free and easy to set up server is FileZilla FTP Server for Windows.