It would be nice if for a limited period of time one could review sent emails as they were sent. e.g., if there are two different revisions of an email and the first 10 people received the first revision and the second 10 received the second revision, it would be nice to be able to see the visual of the email that was actually sent.
This would also be useful if one received complaints from some users about an email not being received or appearing poorly formatted. One could check on the CCB side to ensure it wasn't a formatting issue of the mail merge template.