The full list of elements contemplated by the Exchange ActiveSync protocol can be found at http://msdn.microsoft.com/en-us/library/ee160254(v=exchg.80).aspx. All listed elements are unique and no multiple entries of the same elements are synchronized.
The Zimbra Web Client allows for multiple email addresses to be assigned to a contact. The Exchange ActiveSync protocol contemplates only 3 email address elements, called
Most of the Exchange ActiveSync clients will map the first 3 email addresses assigned to the Zimbra contact to this fields, ignoring any additional email addresses. Different clients apply different mappings, and this is an entirely client-driven behaviour.