You can use the newsletter system to collect email address for use within the Numo Newsletter Compose & Send system, or a third party system.
The Numo Newsletter plugin is great for those sending out to 100-200 recipients at a time. Beyond that, most web hosts will either throttle your outgoing emails with some daily limit, or you will get tagged as sending out blanket emails that could be interpretted as spam.
If you are going to be sending out regular newsletters of 200+ subscribers at a time, it is best to sign up with a white-listed send-service to be sure your emails get to their intended recipients.