1) Go to Tools Options
2) Click on the tab ‘Mail Format’.
3) Click on the tab ‘Fonts’.
4) There are three options available,
• When composing a New Message
• When replying and forwarding
• When composing and reading plane text
5) Click on the tab ‘Choose Font’ for the option you want to configure.
6) Select your default Font, Font Style, Size etc. and click on OK on all three windows opened.