Each time a review request is published, it will send an e-mail (assuming e-mails are turned on for the server as a whole). We want to add a checkbox with the label "Send E-Mail", in the green draft header. If the user un-checks this box before publishing, it will publish without sending an e-mail.

Tested with new diff, checked and unchecked for "Send E-Mail".
Tested with attachment only draft, checked and unchecked for "Send E-Mail".