KBiff is a mail notification utility and its home page is at http://home.sprintmail.com/~granroth/kbiff/index.html.
Are you getting many mails in both mailboxes? If so, it would be better to use two instances to monitor them. If not, then go to the 'Mailbox' tab and click on the little mailbox icon. This will create another mailbox in that instance. Now, whenever either of them gets new mail, KBiff will do all of its new mail stuff....