Succesfully installed Zimbra 4.5.3 OpenSource ed. for Mac OS X Tiger client.
Three times started from fresh install to accomplish this.
After some searching it looks like some questions about OS X installation is still not adressed here, so I will try to share my install process steps here later.

Zimbra is running, both webmail access and IMAP for Mac, but I still have some issues.

Is it necessary to modify hosts file on Mac OS X client, if it is directly connected to internet with correct MX and A records for that IP and Zimbra is running fine? :-)
There are lots of posts in forum about modifying hosts file, but it looks like that its about configurations with split dns and not mentioning OSX at all.

My hosts file currently looks like:

# Host Database
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##       localhost broadcasthost
::1             localhost

So do I need to add my real IP adress there, like:

159.148.xx.xx webmail
or not? (webmail is my machine name, and my setup is accessible from internet under

Thanks for all,