In the application view, click the Discussions tab.
In the navigation pane, click the discussion that contains the message to which you want to reply.
In the table pane, select the message to which you want to reply.
In the Discussions application view action bar,
click 
Reply .
In the body of your reply, click 
Include previous message to include the text of the
message to which you are responding (optional).
In the Message Body text box, type your reply. Use the formatting options in the text editor's tool bar to format your reply.
When you are done typing your reply, click Finish.