Question : Exchange 2003 Account Outlook Mailbox Security

With exchange 2003 how do you ensure that a mailbox cannot be opened or "added" by other domain users in outlook -when they open or add another users mailbox via Outlook Account Settings\Email Account\Change Accounts\Server Settings\More Settings\Advanced\Mailboxes -Add Mailbox. Currently this appears to be allowed even if the mailbox user has a password set to open his mailbox

Answer : Exchange 2003 Account Outlook Mailbox Security

You seem to have permissions set to allow EVERYONE access to everyone else's mailbox. by default, exchange doesn't allow such things - you have to specifically grant another user "Full Mailbox Access" (in AD, properties of the user, Exchange Advanced tab, Mailbox Rights button).

I'd check that setting on one user and see what group you may have given that right to.