Hello Sanford W,
One of my customers has a webpage used for their customers to register their interests in some events, one customer can register for more than one event that he wants to participate,each event has diferent names, locations and this information should be sent by email that marketo will handle.
What I did was an upload via webservice (soap api using importToList), every time we have an insert, then the same customer with the same email will send information regardind two diferent events witch has to be sent by email (a confirmation email), as marketo does not allow duplicates, this customer is receiving only one email with the last imported information, when he should be receiving two emails.
thanks