The procedure for sending an email to all students in a course is slightly different in Desire2Learn as compared to Blackboard Vista. This tutorial illustrates the best practice in D2L for emailing all students in a given course.
From the Course Home Page, click the Classlist text or icon:
The Classlist is the area from which you can send an email to all students. The Classlist defaults to showing a list of everyone in the class, including instructors and teaching assistants. Click the Students tab to see only the students enrolled in the course.
If you have a lot of students enrolled in a course, the Classlist may default to displaying them on multiple pages. If you see a message like the Page: 1 of 2 below, click the dropdown menu and set the per page to 50, 100 or 200 depending on the number of students in the course. The system will remember this setting, so you will only have to do this once.
Now that you have all the students on a single page, you can email all of them by clicking the Email everyone on this tab option.
This will open a Compose New Message window and automatically populate all of the student email addresses in the course. Compose and send your message from here.