MPP can work with Zimbra, as it is still Postfix, but Zimbra's GUI would just overwrite main.cf/master.cf on "Save" and MPP settings would be lost.

All you need is to read /usr/local/MPP/doc/INSTALL.mailservers (skip running configure.pl) and add the options in /opt/zimbra/postfix/conf/{main.cf, master.cf} as described instead of /etc/postfix/{main.cf/master.cf}.

Please see this article for more details.