SMTP Authentication not enforced

[kabal]

Hello all,

I am currently using Zimbra OS
(Release 5.0.10_GA_2638.RHEL5_20081003052615 CentOS5 FOSS edition)

I am trying to setup smtp authentication but I run into a snag.
I set the Enable SMTP authentication from the admin console and also enforce TLS encryption.

If I set require smtp authentication on Outlook Express, it works fine but if I don't Zimbra allows me to relay through it regardless.

I have removed the IP subnet from the Zimbra MTA Trusted Network, and even restarted the server with the hope it would work afterwards, but no show.

What am I missing?
HELP!!!!!

[kabal]

I know there have been a couple of posts on this but I have never gotten any full resolution to this particular issue.
Please help look into it