You could look for the property "report-type=delivery-status;" in the mail header. To read this from the MailItem you could use the code below:
MailItem.PropertyAccessor.GetProperty("http://schemas.microsoft.com/mapi/proptag/0x007D001E")
To traverse the mail items you could look at an article I wrote on saving mail items to separate files.
Save all Outlook Mail Items to separate files[
^]
Good luck!