Create a Smart List to find out, first check if the email stats are right:
- Was Sent email "confirmation email"
That should give you the same number of in the email performance report (assuming you look at it in Lead Management, not in RCA which is only updated overnight).
Then compare the registrants with the emails in a Smart List:
- Was Sent email "confirmation email"
- NOT member of Program or Filled Out Form (depending on what you're looking at)
Or the reverse:
- NOTWas Sent email "confirmation email"
- member of Program or Filled Out Form (depending on what you're looking at)