cancelled or altered appointments result in users not being known.
 

We have a single user that will send out an appointment to a group. Then
after a short while he will either cancel the appointment or alter it. When
the change or cancellation is performed, a few user accounts show up in a
confirmation email that their account did not exist within the domain, even
though they do. The user accounts in question are randomly identifed,
meaning that 2 of them may be listed this time, whereas another time all
three are listed, or maybe only one will be listed.

We are running outlook 2002 SP3, and Exchange 2000 SP4