It depends on if you're going to be using the OSE or NE edition of Zimbra.
OSE has no 'native' support beyond IMAP or POP3 for smart phones, and I think the support for viewing single pages on large attachments would be a mail client feature and neither of my two mail apps for Android allow me to view only the page I'm on.
They both download the attachment before showing it to me.
Ben Franklin quote:
"Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety."