The Do Not use Rich Text option is available for email messages that need to appear in plain unformatted text. You use the Do Not use Rich Text option when your recipient cannot receive HTML formatted text.
From the Compose Message window, select the Do Not use Rich Text option. When you use this option, the Rich Text toolbar does not appear. Your message will be composed in normal ASCII text format. No formatting can be used to highlight or stylize the text. Also, the Spell Check feature is not available with this option.