Plain text in Mail.app by default

I generally prefer plain text when writing emails. However, in the place where I work, a lot of people use Microsoft Outlook or its web version. By default, it sends out emails in HTML. Even worse is the fact that the font size in those emails is too small. To reformat all incoming email and display them as plain text, quit Mail.app, type

# defaults write com.apple.mail PreferPlainText -bool TRUE

Relaunch Mail.app and enjoy.

To revert back, use

# defaults delete com.apple.mail PreferPlainText