How do I change the recipient e-mail address for a meeting request

Outlook 2003 / Exchange Server 2003.
The Problem is that I have a user that sends a meeting request out to a
user, after the reciepient responds to accept the meeting the originator gets
the approval for the meeting and the meeting reciepient then gets a E-Mail
failure to another user's e-mail in the company that is no longer here. And
their e-mail address and account have been deleted. So it makes sense that
the mail delivery would fail. But wher is this information in the
originator's outlook setup? They get a good response from the acceptor. The
problem is that the acceptor gets this e-mail delivery failure notification
from a non-existing account. Like the the meeting request is being sent from
a group or something. Does anybody have any ideas? The other user and the
current user used to share each other's calendar.