You can leverage the EmailMessage
Message Class ItemSchema.ItemClass
property to determine what type an item is. Here is a snippet to help you out...
FindItemsResults<Item> mailItems = inbox.FindItems(new ItemView(1000) { PropertySet = new PropertySet(ItemSchema.Id, ItemSchema.HasAttachments, ItemSchema.Subject, ItemSchema.ItemClass) });
foreach (EmailMessage message in messageItems)
{
if (message.ItemClass == "IPM.Schedule.Meeting.Request")
// we have a meeting request
}