Together with Elastic Email, MailChimp is a very popular way of sending large amounts of mails for newsletters.
Simplenews is the module to end newsletters. When sending large amounts of mails this is the more professional way. MailChimp has his own mailservers that are quick and avoid spam.
This module lets you to send newletters from within your Drupal site. You pay less than 1 dollar pro 1000 mails. In a few minutes one can send thousands..