Up until now, the Mail app allowed us to change the font and font size only while composing an email. For instance, I like the Palatino Linotype font and set it as the default font in Word, Evernote, and other frequently used applications. While there is nothing wrong with the font, there are users who like other fonts and would like to use a different font instead of the default font. Windows 10 Mail app uses Calibri as the default font. The Mail app has evolved over the past three years and offers all the features that you would find in a good email client. Mail app is the default email client in Windows 10.