It's weird. I got a NDR from non-existant user when I sent meeting request to my team members.some of my team got it too.The non-existant user was also team member but did quit long time ago.Below is the NDR.Thank you Your message did not reach some or all of the intended recipients. Subject: MS SQL 2008 Introduction Seminar The following recipient(s) cannot be reached: Kim, Joakyum on 2010-03-08 4:40 The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address. <spkrcms00001.kr.intranet #5.1.1>

It sounds like one of your team members still has them as delegate on their calendar. MAPI permissions don't get cleaned up automatically when someone is removed from the directory.

I can reproduce the NDR in my lab.If you send a mail to user1, user1 has an outlook rule to redirect the mail to user2, but if user2 was deleted, user1 will receive the NDR.So if you send a mail to your team's group address, I guess you and some team members who get the NDR has the redirct rule. Please check.You can also log the rule events in the Event Viewer.I suppose your exchange server is Exchange 2003.1,Start Excange System Manager, located to the server who host the mailboxes of the users.2,Right click the server, click Properties3,Click Diagnostics Logging tab, select MSExchangeIS->Mailbox in Services section, and then set the Logging Level to Maximun for the category Rules 4, click OK.Then reproduce the problem, check the event ID 1037.Frank Wang

Also see:http://support.microsoft.com/kb/312433Accepting or denying a meeting request causes a "5.1.1" non-delivery report in Exchange ServerThe KB mentions mdbvu32. Note it has been replaced with mcfmapi.