Debbie -
Welcome to the forum.
The file type '.ES' isn't a recognized file format, or MIME
type, so your users would just get a 'HTTP Error 404 - File or
directory not found.' message.
You could add the MIME type on the server. In MS's Internet
Information Services, in the MIME types; add 'ES' as 'Text/Plain'.
Then restart IIS.
But, that could be an 'issue' for some, such as the
security-minded.
Better yet, you can change the files extensions themselves
to something else; .txt, .js, .xml, or compress them and deliver
them within a .jar or .cab file.
Better than messin' around with them mimes, I tell ya.