On this page, you can send mass e-mails through the e-mail queue. A mass e-mail is an e-mail that will be sent to a large number of recipients.
Using the Site drop-down list, you can select which site the recipients are related to. Based on this choice, users can be selected either directly, or according to the roles or groups they belong to by using the Add users buttons in the Recipients section. If you choose (all) from the site drop-down list, only the users section will be displayed as roles and groups are always site-related.
If you are accessing this tab from CMS Desk, only users, roles and groups from the current site can be selected.
You can also add an attachment to the mail using the Attach file link at the bottom of the page.
More resources can be found at Developer's Guide -> Modules -> E-mail queue -> Overview.