Suppress the Magento newsletter (un)subscribe emails magento help3
This is vital since there is no way to test email templates. To test I recommend unsubscribing all subscribers, testing and then re-subscribing them. Painful, but at least with this fix you can stop everyone getting emails.

Edit the file app/code/core/Mage/Newsletter/Model/Subscriber.php and comment out any line with ->send in it.