Does it matter if all users have access to those defined groups? User Groups, in SmarterMail terms, are really Groups set up for, and with, specific permissions.
A Contacts Public Folder may be more in line with what you want to accomplish as that's added at the domain level and then it shows as a Contacts Folder for users. That should sync via MAPI & EWS to clients.
Derek Curtis
COO
SmarterTools Inc.
www.smartertools.com