This feature enables you to send simple mail to a bunch of users (Enterprise only). Emails can be simple or using a template, including tags or not. Using this feature you have to know that no data will be saved on your website, including no statistics.
Please don't use it to send your newsletter to users, use it only as testing purposes.
How to send an email using Simple Sending feature ?
First select your users with the input at the top of the page. Separate emails using space character.