Open Outlook
Go to File
Select Options
Click Mail
Under Compose messages, click Stationery and Fonts
In the Signatures and Stationery window, choose the Personal Stationery tab
Click Font under New mail messages
Select your preferred font, size, and style
Click OK
Click Font under Replying or forwarding messages
Select your preferred font, size, and style
Click OK
Click Font under Composing and reading plain text messages
Select your preferred font, size, and style
Click OK
Click OK again to save changes