Outlook .ics attachment- ICalendar

I am sending mail from .net web.Mail to outlook with .ics file attached. I have an appointment in this .ics file. I am receiveing this mail in Outlook but the appointment is added to the Calendar only after I open the mail and the .ics attachment. Can I know how to add this appointment to Calendar without opening the mail in Outlook, Of Course I have to use only ICalendar Format Not Outlook.Application or so Object from .Net