Apple Mail shows plain text instead of HTML email I have a gmail account setup as IMAP in Apple Mail and recently some new emails coming through have displayed the plain text version instead of HTML. If I check the same email through gmail.com it shows the HTML fine but back in Mail I can't even change it to HTML under View -> Message -> Next Alternative.

This solution did not work for me:
defaults write com.apple.mail PreferPlainText -bool FALSE

I'm running Apple Mail 5.2 on Mac OS 10.7.3

I have just found that the same email message will show HTML when viewed in the All Mail Folder but not when viewed in the Inbox.
I opened ~/Library/Preferences/com.apple.mail.plist in Xcode and searched for PreferPlainText.  It seems to want either YES or NO as a value.

I set it to NO and saved, then relaunched Mail.app.

HTML (Rich Text) mail is back.