Firstly, I am trying to setup zimbra using two machines. One will handle the spam/virus filter then deliver the filtered mail to another zimbra machine running the mailbox and ldap services. I noticed that on the spam filter machine, the file contains
hostname => '@@zimbra_server_hostname@@',

which I had to change it to the line below in order to get the filter machine to use the ldap server running on the mailbox machine for amavisd.

hostname => '@@ldap_host@@',

When I installed zimbra on the filter machine, I told it to not setup ldap service and gave it the address of the second server as the ldap host. Apparently, that change was not applied to the file. So I am wondering if I did something wrong or this might be a bug in zimbra installation script.

Secondly, how do I set up the filter machine to deliver processed messages to the zimbra server containing the mail stores?