hrm. disecting com_zimbra_url i found it does support file:// hyperlinks. I sent this to myself.
This is a valid pdf in my home directory. It shows up as a hyperlink when i receive the e-mail, but clicking on it does nothing. Right clicking on it and saying 'open in another window' does nothing either. However, if I copy it and paste it into the address bar of another tab then it opens the pdf fine.
Is this a browser problem? I tried the same thing in IE and FF on windwos as well using like file:///c:/temp/test.pdf and same thing, it comes through hyperlinked but ntohing happens when you click on it.