To open Preferences and get the Fonts & Colors pane

• From the Mail menu, choose “Preferences…,” then click Fonts & Colors.
  
  

  Choose default font sizes.

  

  Message list font is the font used in the list of messages on your Mac.
  
  Message font is the font in which you will type your email messages. If you choose a font that your recipients do not have installed on their computers, this font you choose will turn into their default fonts.
  
  Use fixed-width font for plain text messages: When you choose to receive or write messages in “plain text,” which is totally without formatting or other typefaces, this is the pop-up menu of fonts that are suitable.
  
  Color quoted text: Email replies often contain quotes from previous emails. Color coding and indenting the quotes helps visually organize the message in a hierarchy of responses. To apply color to quoted messages, check the box, then choose colors. See the example on page 459.