Classroom emails can be sent to an entire class, a selected group, or to individuals.
Click the People tab.
In the list of students, you see a check box next to everyone's name.
Select individual students or check the Select all check box.
You are limited to emailing 100 students at a time.
Click the Actions button.
There a few other options in the menu you might find helpful. If you have a student drop your class or move away, remove them from the class. If you've allowed students to post or comment on the Stream page but have one or a few students who are abusing it, mute them. They won't receive a notification; they just won't see the option to post.
A Gmail message opens in a new browser tab. All the students you selected are listed in the Bcc field. Names are populated in the Bcc field rather than the To field in order to keep the recipient list private to those who receive the email.