I've searched the forums, but I apologize if I have missed something obvious. I've seen threads, like Local relay which seek to restrict local relay to authenticated users, but not exactly in my situation.
I understand a mail server normally needs to allow unauthenticated users to send mail to local mailboxes to facilitate the normal operation of E-mail, but I still wish to restrict local relay to authenticated users, or local network hosts only.
We have a spam firewall device at the edge of our network that we use to receive E-mail from the internet at large, and it does a fantastic job of filtering spam which in turn reduced the load on the Zimbra server, everyone is happy.
The only problem is, Zimbra allows any spammer clever enough to waltz right in and bypass the spam filter, if they connect to the zimbra SMTP server directly. Of course they can't relay to the general internet, but they can spam all of our local mailboxes with impunity.
I know I could restrict access at the network level, and require my legitimate clients to relay through the spam filter as well, but I would prefer leaving the setup as it is, and just requiring Zimbra to enforce authentication for ALL users.
Is there ANY way in zimbra 6 to have this restriction? I am not opposed to hacking around in the postfix configuration every time I upgrade if that's what it takes.
Thanks for reading, and doubly so for any assistance you can provide!