just to verify, you're not trying to send to soemone on your zimbra server right? that will always work
If your server is setup to accept mail for woopty.com, and I set your server up as my smtp server, i'll always be able to send e-mail to
someone@woopty.com. This is because really i'm not doing anything more than another mail server would be doing.
However, if I"m using your server as my smtp, i should not be able to send email to any other domain, thats where it should error with relay denied.