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I would like to at least make my smtp authenticate the user before it sends it mail. It currently works fine without any user authentication or SSL. anyone can relay to my server and use port 25. How do I make authentication before sending any mail?
Nobody can use your server as a relay. Local users on your LAN are automatically trusted, do they not have to enter login details? That's the authentication they use, authenticated users can always relay through your server where ever they login from. If you want to change that behaviour of Zimbra to use SSL please search the forums or wiki for details on how to do that.
No login details. That is what I mean. For example I have my outlook setup to send out mail without the "My outgoing mail server requires authentication button" checked. I am still able to send out email. And I am not on the same subnet.
If you are not entering any login details then the ZImbra server has been set-up to recognise your subnet as a Trusted Network. What is in the "MTA Trusted Networks:" section of your Admin UI and what are the subnets that can relay?
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SMTP sends without user authentication 
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