I'm not able to get my zimbra server mta service running

I've tried several things (I thought they were related to my problem):

stop zimbra
/opt/zimbra/libexec/zmfixperms -extended
start zimbra

change nsswitch.conf db files to files
None of them have worked

In the /var/log/zimbra.log I see this error:
Dec 4 09:54:48 srvzim1 postfix/postqueue[23206]: fatal: Queue report unavailable - mail system is down

Please Help!