Opening a file on the IFS via email link

I am sending out an email to my users after they've converted a database
file to CSV format. In that email I include the URL link to the file on the
IFS, as follows:

  Your file is available by clicking on the following link:

   file:\\mydomain.com\ifsfolder1\ifsfold2\yourfile.csv

The problem is that some users (most?) can not click on the link and have it
open Excel. In stead, it does nothing or gives them a message box that says
"Cannot open file...".

By changing some user IDs and passwords to the AS/400 to be the same as the
network user ID and password, it seems to work. But for others it does not.
I don't know what area to look in to try to resolve this issue.
Any suggestions?
-Bob