You can message a user in your account.
In Global Navigation, click the Courses drop-down menu [1], then click the name of the account [2].
Locate Find A User on the sidebar. Type in the user's name [1] and click Go [2].
After clicking Go, you will see the search results. To access that user's details, click the name link.
Find and click the Message [User Name] button. By clicking on the button, you will be taken to your Inbox to send a message to that user.
Note: You can always use your Inbox to send messages.