One of the settings for the Dialogue is Mail Default: Yes/No.

This doesn't really give many clues as to what this setting actually does. Reading the attached context help suggests that this will control whether a notification email is sent or not.

To my ears default suggests that it can be overriden somewhere, perhaps on a case by case basis, or by user preference. It appears this is not possible so I suggest changing it to something like:

Send Notification Email: Yes/No