A meeting update message or a meeting cancellation message from an Exchange 2003 user is not delivered to external attendee
It was brought to my attention that there is a random issue when a user cancels a meeting and some of the attendees are not notified via a cancellation. Upon digging further, the users that are not receiving these cancellation are found to be external users.
Conversation with the IT folks in these users' companies are that their messaging infrastructure is running on Lotus Notes and Exchange 2007.
The issue has been found to be that of the below and the procedures listed can be used to check if the issue is affecting your Exchange 2003 setup.
When sending meeting changes or cancellations to another mail server outside of your exchange 2003 organization messages get stuck in the queue and if the diagnostics logging of the MSExchangeTransport component is set to maximum, the following warning is logged: