How do I modify the settings for Messages?
This feature allows users to modify the default Messages tool settings. Users with site owner permission have additional options for configuring the tool within the site.
Site Owner (Instructor) Settings Options:

As an instructor or site owner, you can choose whether or not site participants are able to forward messages, and which groups (if any) are hidden in the message recipient list.
You may also set a personal forwarding email address for your own messages.