Server side rule not working

[wli2k2]

I created a mailbox user and a distribution list. I then placed the mailbox
user into the DL. I logged in as the user and created a rule basically
saying any email sent to the DL will have the server reply with a specific
email message.

However, since this is a server side rule, Outlook does not have to be
opened, right? The autoreply does not get sent if Outlook is open or closed.
However, the autoreply does get generated if we open the mailbox and click
the "run rule now".

Any ideas why this is happening?

Thanks.