Do any of the following:
Change a font in the current item
Note This procedure is not available in messages if you use plain text as your message format.
Change the default font for new, forwarded, and replied to messages
Note If Microsoft Word is your e-mail editor, you can set the default fonts in Word, too. If your message is in HTML format, you can even use a cascading style sheets (CSS) to define the fonts. For messages you reply to or forward, Word can also automatically choose a different font color to distinguish your message from the previous one in an e-mail discussion. For more information, see Word Help.
Change the default font for reading international messages
This font is used for plain text messages and for HTML messages that were not formatted by the sender.