I'm using Zimbra 5.0.16 opensource edition and all was working fine until I had a little hickup a few weeks back with some people attempting to use my system as though it was an open relay.

That seems to be all fixed, the only problem however is that now no one that is connected to the server can send emails from it??

I have 2 internal subnets using prefix and they included in the Zimbra Postfix main.cf file too under mynetworks along side the loopback address.

I have managed to gain some success in sending SMTP mail through the secure port on the server as I'm in a remote location but internal clients don't have any ability to send either meaning that something's up.

/var/log/maillog doesn't show anything and the MUA, Seamonkey or Thunderbird just claims that the server either can't authenticate or that it isn't an openrelay??

What's going on as all mail servers should be able to relay SMTP mail for registered users?

The system used to ask for a password beforehand but subsequently gave up on the last few attempts. Since it's impossible for a system to alter overnight or change configuration by itself, something seems to have affected it but I can't work out what.

Has anyone experienced something similar to this before or does anybody have a clue as to why this is happening??

All my users currently can't send mail unless they use the webmail AJAX or HTML interface :-(