I got Zimbra installed (6.0.2 build 1912 network edition, Ubuntu 8.04.3), added some users, able to log into web client as users, able to sync a user's account with their phone, etc. - everything is working well except no incoming or outgoing mail is going through at all. Contacts and calendar syncs with the phone, but no mail. Sending emails between internal users doesn't work either (using full addresses, e.g., anuvatec@example.com). Internal users don't get email/notifications when another internal user adds them to a calendar item.

Telnet'd into mail server (telnet mail.example.com 25) to send a test email but got the following error:

rcpt to:apersonalaccount@gmail.com
554 5.7.1 apersonalaccount@gmail.com: Relay access denied
Any ideas how to get mail flowing?