I could send mails from a zimbra account to another zimbra acount without authentication... Is this how it should work?? So people can send dupe the senders id and send junks..
I am totally new to Linux and ZImbra & administering..
Yes, that's exactly the way it works. You should be able to send an email from one internal user to another internal user, it's called the 'Trusted Network', have a look in the wiki for the word 'mynetworks' or search the forums for some more details.