OK, let me explain my situation:
I want to use Zimbra to retrieve/send mail from my domain (mydomain.com) whose email is hosted by Google Apps.
I have the following:
CentOS 5.1 with Firewall and SELinux off with the hostname is apollo
Zimbra 5.0.2 GA 1975 RHEL need to be installed on my CentOS box.

I have two servers in my company, one act as the DNS Server (BIND) and another is used to install Zimbra .
The DNS server have some A records point to some IPs in my LAN with a suffix mydomain.com. Eg: the host abc and abc.mydomain.com will resolve to the same IP in my LAN.
This DNS server has NO MX record for my domain. It use OpenDNS.com DNS servers to resolve other domains.
Right now, we are using GoogleApps for our emails. ie, Google will host emails for my domain.
When I install Zimbra, it complaints about not able to find a MX record for my hostname (aka apollo, it does can resolve that hostname, because the DNS have an A record for that hostname) and suggest me to change the hostname. When I change the domain to mydoman.com, it now can list some MX record of Google, but it still complaint about none of MX record for my domain (mydomain.com).
That's the problem when I install Zimbra.
Any help will be appreciated
Sorry for my bad English, because English is not my native language