Iterative mailer testing requires reviewing and deleting the mail queue each iteration.
The number of emails generated can be large, and the existing queue delete scope is to delete only those emails displayed.

On my site, attempting to display and delete 500 emails or more will fail and I'm kicked out to the Joomla system dashboard.
Having a Delete All button would make testing much easier, regardless of the list display setting.

Also, there doesn't appear to be a way to view a single queued email, to review and validate the email contents as correct.
A "View Selected Email" button or having a list field linked to that feature, would be very helpful in testing.
Thanks,
Fred