Hi,
Most likely the files got messed up in e-mail.
The KML file is simply a XML text file that conforms to the KML
standard.
You can hand-edit the file in any text editor then try again to open
it.
The beginning of the file should start with something like this:
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="
http://www.opengis.net/kml/2.2">
<Placemark>
...