I've recently made changes to the Epinova EmailObfuscator project. The new version supports UNC paths.
Previously, you had to store the images in a pre-defined virtual directory. With the newly comitted changes, you can save the changes to a UNC path wether it is a local server path, e.g. c:\vpp_folders\emailimages or a file share eg. \\myserver\sharename\emailimages
This is really usefull for sites in a multi-server environment! :)
Have a look at the module and download the code here.