I had an odd problem with my third Zimbra install that I am not quite sure if it is a bug or something to do with my system (More likely the latter given the corrective action).
I have installed the open source edition on FC5 just fine, no issues with the install. I am using a non internet domain name with a local BIND DNS server for testing due it being a new edition.
Everything worked hunky except for the MTA part of things. It constantly refused to accept mail or send mail despite the fact it started without problem. However when I connected into the machine via telnet on port 25 I noticed it was identifying itself as Exim instead of the usual postfix!!!
Here is where it got confusing...
Using my webmin console I decided to disable Exim from starting up to see what would happen and boom...everything on Zimbra stops working apart from the logger and LDAP.
Whoops....I renabled Exim and....everything starts working again!!!! Including the MTA which when logging in via telnet now correctly identifies itself as Postfix.
I'm at an utter loss to explain how all this came about as I certainly did not take any knowing action to put Exim on my system and it wasn't there from install. Anyhow I uninstalled it and then everything began to work fine.
Just thought I would share this with you in case you encounter a problem with the same symptoms. ;-)