How do I add new people to an existing conversation as an instructor?
You can add people to an existing thread in the Inbox.
If your recipient list contains more than 100 users, your message will automatically be sent as individual messages to each user.
Note: When adding users to an existing conversation, you cannot change the course or the subject line.
Start to type a name in the text field , or click the Address Book icon  to filter by users or course groups.
Verify you added the correct person.