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.
1. In Global Navigation, click the Inbox link.
2. In the Inbox filter, select an existing conversation.
Select a Conversation_Inbox [View Image]
3. Locate the message thread and click the Reply icon.
4. Start to type a name in the text field , or click the Address Book icon  to filter by users or course groups.
Add User to Compose Message_Inbox [View Image]
5.Enter a reply in the text field. Then click the Send button.
The link will update the total number of people involved in the conversation.
Newly added participants will be able to read and comment on the entire conversation, even the messages that were posted before they were added.