Non-exchange email server. Outlook 2007 user sending meeting request. Outlook 2002 and Outlook 2003 users trying to accept request.

When accepting/replying to a meeting request, I have two users (Outlook 2002 and Outlook 2003) that get an error message that the reply is Undeliverable. Another Outlook 2007 user was able to accept the meeting without error. The two user's having trouble can email the meeting organizer without errors and they can also accept meeting requests from other organizers just fine.

When I look at the logs on the email server, the RCPT TO: field has the meeting organizer's name instead of the email address. (i.e. Tom Smith instead of tom.smith @ mydomain.com). Is there a reason Outlook is formatting the return address this way for a meeting reply? Can I fix it?