One of our users, using Outlook 2007, is trying to send an appointment to another user who is using Lotus Notes. The calendar item gets stuck in our Exchange 2003 SMTP queue and eventually the delivery fails. Emails sent from Outlook 2007 to Lotus Notes are delivered fine. As a test, we sent the same calendar appointment to the same Lotus Notes users using Outlook 2003 and it seems to have been delivered just fine. I can't seem to find anything online regarding this issue. Any assistance would be greatly appreciated.