Thanks for thinking of this, I am surprised that more people haven't done something similar.
I have installed it on a windows xp machine and it works fine, as far as it goes. The menu option is visible (although a different font to the other items) and choosing it opens a new message window with the UNC path of the file. Unfortunately with Thunderbird, the UNC paths that it generates are not "clickable" for the recipient, which introduces another step in the process of opening the file.
I have just installed a minor modification ( http://blogs.sun.com/alanbur/entry/maki ... ks_work_in
) to Thunderbird to allow it to open file:// links. I have noticed that the short cuts that explorer generates are file:// links. I don't really know why one might choose UNC or file:// links but I know that unquoted UNC paths are not recognised as anything but text by thunderbird.
I assume that you have tested it with Outlook and it does what you want. I don't know how Outlook would deal with URI rather than UNC paths. If it was able to deal with them I can't imagine that modifying the code to generate them would be that hard.
Once again, thanks for the great idea.