Hello Randy,
The protocol itself (ActiveSync) was primarily created to work on mobile devices and this would cause problems on the desktop app while, for example, moving messages between normal (IMAP/EWS) accounts and the ActiveSync account. On top of that, the royalty fee that is charged by Microsoft for each installation is unfortunately incompatible with our FREE license.
We tried to convince the Zimbra team to support the well-designed Exchange protocol but they refused to do so.
Best regards,
Russel