Ok, you set an MX record for your domain in your internal DNS server? It should point at your zimbrabox.prockop.local hostname.
You're still in the midst of your installation, correct?
I also found this thread about using .local in your hostname. You really should make the hostname what the public name will be so SSL certs match, etc.:
http://www.zimbra.com/forums/install...ving-mail.html