We have made a howto about making Zimbra OSE to work in High Availability mode thanks to Pacemaker, Corosync and DRBD according to 2012 year state of the art.
I've opened a new thread so that this thread either can focus on old methods based mainly on heartbeat or maybe other people just link to new ways of doing zimbra HA on drbd as I'm just doing.
That means that questions and doubts on e.g. how to use the ocf zimbra script should be asked on the new thread.
Zimbra on Pacemaker + DRBD howto