On the Subscribers.Standard tab, I have selected the subscriber list (based on a query)
On the Subscribers.Advanced tab, I put a checkmark in the email box for "user" and mapped it to the email field (in the "Message Break Field / Database Lookup Value" section). In the "Deliver to a specific..." section I selected "contains email address to send to" and mapped it to the email field.
There are 3 subscribers on my test list; myself and 2 colleagues. We each got 4 messages - 2 for ourselves and one for the other 2.