You can customize the font style used in new messages and replies. You can style them both the same or create a distinct style for replies separate from the new message style.
You can also change the layout of the original message text in your responses.
Click the File tab.
Select Options.
Click the Mail category in the left pane.
Scroll to the Replies and forwards section, then click the list arrow for When replying to a message or When forwarding a message.
Select how you want the original message to appear.
Click OK.
Now when you reply to or forward a message, the original message will be formatted to your specifications, making it easy for the recipient to differentiate the response from the original message.