Saving a message

Saving a message

Hi there

I am a little confused about how mail messages are saved and how to open them. Can somebody explain please. In short the problem I have is this:

When I go to a message and select Save I get the standard Firefox "What do you want to do with this" type dialogue box which says:  

 msgxxxxxx.html.zip
which is a: ODT document
from http://mail.zoho.com
"What should Firefox do with this file"

I save the file to a folder and it is saved as  .zip file.

However, if I use a Zip utility it just get an error but if I use an application that can use .ODT such as OpenOffice it does open but I have to select the application manually. (i.e. OpenWith)

Am I saving it correctly? Why is it a .ZIP extension if it needs and .ODT compliant application to open it?

Confused and cold of Bristol, UK.