Sorry Jason, I misunderstood.
So the page needs to stay open to redirect to the success page, but not for the emails to be sent?
At the moment the success page includes a button to reset an Email field back from Yes to No. So if some of these mail shots are going to take a while it might be a plan to move that function to the start of the process rather than the end.
And also set the link to the page that sends the emails to open in a new window so that if it is closed the previous page is easily accessible.