Users able to view other Inboxes without delegate permissions

I just started this job about 2 weeks ago and I’m coming across some strange things. Here’s the one that is troubling me the most at the moment.

Small office setting, running Exchange 6.5 and Outlook 2003 and everyone was setup to be delegates for calendar/contact sharing, but a few people could view other user’s inboxes. So I removed delegates from permission lists and that seemed to clear things up for everyone except one individual has no one entered in the delegates permission list but everyone can view her inbox.

Really strange stuff…Are there any policies I can change to affect these permissions rather than going to every desktop to verify. And how can I cease all users from having viewing rights to a non-shared inbox?

Thanks in advance