How do I message students who have not signed up for a self sign-up group?
If you have created a self sign-up group within your course, you can message students who have not yet signed up for a group and remind them to do so.
Verify that self sign-up is enabled for the group set  and that unassigned students exist for the group set .
Click the group set Options menu , then click the Message All Unassigned Students link .
Note: The Message all Unassigned Students link will not display if all students have been assigned to a group.