It very easy to change the font style in outlook for Mac 2016 on OS X. Follow below steps to change the default font. Open "Outlook" application on Mac. Open Preferences of Outlook 3. Click on Fonts to change the default font settings for the outlook. 4. Select the desired font to set as default font. 5. Close the preferences window. 6. Click on New Email, Now your default font would set to the newly configured font style.