If you want to delete all subscribers from a mailing list (eg. for a One-Off e-Newsletter), follow these steps:
***Important: Deleting subscribers will PERMANENTLY delete them from the list that they are on. In deleting them you are also permanently deleting any subscriber statistics (eg. what emails they received, what links they clicked on, etc.).
1. Go to System Admin > Email Lists > Drop Subscribers.
2. Select Newsletter List from which to drop the subscribers.
3. Select “Yes” to dropping ‘dead’ subscribers.
4. Click “Next”.