Originally Posted by KevinH
Check in the admin console under the MTA config the you have DNS lookups off and don't have any of the reject domains settings on. For a system that's setup correctly in DNS you shouldn't have this issue. Might be due to your local network setup. Seems postfix is not recognizing attic.local as a domain. Is that your machine name? Or did you install the system with the mail domain of localhost.localdomain?
The Zimbra installer and code doesn't change or modify the system clock. You may want to verify you have ntpd running.