Do you offer a way to send newsletters?
If you are planning to send out a high volume of emails, or a small volume but need a really easy to use system, we recommend MadMimi.
We also offer several pre-installed-scripts that you can install through your control panel. Scroll to the bottom and click on "Softaculous" and then browse the "Mails" section. Software specifically for newsletters includes phpList, poMMo, Webinsta Maillist, ccMail, and OpenNewsletter.
Additionally, many scripts like Wordpress, Drupal, Joomla, Zen Cart and others have their own plugin system and have newsletter plugins available that allow much tighter integration with your user or customer list.