iCalendar email causes meeting duplication

[evaleah]

I have implemented code to send an iCalendar formatted email from the web. My users want to be able to send multiple invitations to the same attendees for the same event over an extended period. Basically, they want to send out the initial invitation and then reminders. The issue I am running into is if a user accepts the first invitation and then later receives another one and accepts again the same meeting appears in their Outlook calendar twice. Does anyone have any idea of how to check for the existence of the meeting in the calendar before allowing it to be added again?

 

Thanks!