What is the meaning of the red, orange and green envelopes next to the students?
If you go to my students and open a group, you'll see the list of students, and an envelope next to each student.
The green envelope means that the student has registered his/her email to receive notifications (homework, feedback).
The red one means that no email is registered (the student needs to log in to receive notifications).
The orange one means that the student has registered his/her email, but not confirmed it (will not receive email notifications until the email is confirmed)