I have setup the OSS version of Zimbra on a CentOS 5.6 host. I have configured external directroy authentication and got the syncing between my OpenDirectory server (OSX) and Zimbra working.
Now, since I want to test drive Zimbra first, I am not yet ready to make the swtich-over from my OS X server, that is currently serving as my mail server.
To achieve this I have setup my postfix mx to double all messages and forward them to either my current mail host and to my zimbra host. So incoming messages that target email@example.com split to firstname.lastname@example.org and email@example.com.
However, my Zimbra server rejects these messages with a "Recipient address rejected: User unknown in relay recipient table;", since the main domain on my Zimbra server is example.com as well.
I might resolve this by tweaking Zimbras' postfix config, but I thought that there would be a way to configure this in we WebUI, since I don't know how it will react to changes to it's config files that were injected, bypassing the WebUI.