Sorry i do not know what Zimbra is. But if it cannot connect then there is likely something preventing it. I would check firewalls on both machines, firewall devices between the two, port numbers, DNS, services on the remote server (Zimbra). I'm presuming that its some sort of email server... so I would check the logs on both ends to see if there is more information regarding the issue. I would setup a stand alone email client (Thunderbird, gmail, etc) and test the settings and see if they work.
