should this file be empty?
I just did a fresh install of zimbra 4.5.4 and it doesn't work at all.
my logs are pointing to this as an issue:
Mar 29 04:40:01 server postfix/postqueue: warning: My hostname server is not a fully qualified name - set myhostname or mydomain in /opt/zimbra/postfix-2.2.9/conf/main.cf
Mar 29 04:40:01 server postfix/postqueue: fatal: Connect to the Postfix showq service: Permission denied