A meeting update message or a meeting cancellation message is not delivered.

One of my user complained that he wasn't able to send a meeting update or meeting cancellation to any outside recipients. This is a big issue in our company because the organizer coordinate schedules of 5 to 25 (even more) consultants in the field. If they received the initial meeting schedule but not the cancellation or meeting update, then the coordinator is in trouble.

In technical scenario. A Microsoft Exchange Server 2003 and a Microsoft Exchange Server 2007 organization exchange communication. An Exchange 2003 user organizes a meeting and then send a meeting requests to an Exchange 2007 user. Then, the meeting organizer uses Microsoft Outlook to send a meeting update or meeting cancellation message to the Exchange 2007 user. The update or cancellation update is not delivered to the Exchange 2007 user. To troubleshoot this issue, you can check your Exchange 2003 SMTP queue where you can see this update or cancellation message still waiting to deliver.

How to fix this issue? Microsoft already received a lot of complain about this issue, so the Hotfix is already available for you. Here's the link: http://support.microsoft.com/kb/938650

There is also a way "Let me fix it myself" guide on how to accomplish this task manually, also included in the KB938650. Here's the step-by-step guide:

1. Click Start, click Run, type Regedit, and then click OK.
2. Locate the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\InternetContent\MimeHandlers\{85D2DDB8-6225-11D2-BDF1-00C04FD655B5}
3. On the Edit menu, point to New, and then click DWORD Value
4. In the details pane, type FixRecipientTrackStatusTime for the new value, and then press ENTER.
5. Right-click FixRecipientTrackStatusTime, and then click Modify.
6. In the Edit DWORD Value dialog box, click Decimal under Base.
7. In the Value data box, type 1, and then click OK.
8. Exit Registry Editor.

The server will not require to restart the server but I highly recommend it to make sure that everything is working as expected.

References:

Microsoft Exchange Server 2010 Best Practices (Best Practices (Microsoft))

Exchange Server 2010 Unleashed

http://support.microsoft.com/kb/938650