The Messages tool allows you to reply to a message sent to you by another member of the course.
In the target Sakai site, select the Messages tool from the Tool Menu.
Choose Reply or Reply to all.
Select Reply to reply to the author of the original message. (Or select Reply to all to reply to all site members included on the original message.)
Compose the message and send.
Compose the message and select Send. For instructions on composing a message, view the article How do I send a message?