This install is integrated into Outlook and really wants to install in the user space. The setup.exe installer extracts files into the user temp space and even extracting the files and locating them with the installer causes the setup.exe to fail if running viat he system account.
There are a couple options we've found: install into user space with SCCM. (that's the one we chose). There are several MSIs that extract that are setup-driven; you could fix that and see what happens.
Information on deploying this is found in their admin manual located at http://www.google.com/url?sa=t&source=web&cd=1&ved=0CCAQ_hIwAA&url=http%3A%2F%2Fwww.cisco.com%2Fen%2FUS%2Fdocs%2Fsecurity%2Fesa%2Fplugin%2FCisco_Email_Plug-in_7.1_Admin_Guide.pdf&ei=mHtOTtyADqq1sQLG0v3_Bw&usg=AFQjCNHoFqpM7b89bO-hYAumcs-gtILiyw; see page 31.