Hi Steve,
I seem to remember IMAP is an option when you first install SME. It is nice and easy to setup but be careful which client you use, I would advise getting your users to use webmail, as pretty much everything else has problems conforming to the IMAP standard. I use Outlook, and it has problems, but my users don;t like webmail, doh!
I have the same problem, and have all but given up on the global address book. I couldn't get ACAP to work, and tried using LDAP, and that was closest to what I needed, so that may be worth a look.
HTH
MattSteven wrote: