Mail won't display HTML mails

The Mail.app does not include a setting to automatically view or change HTML formatted messages to Plain Text.

If a spam message or any message is automatically marked as Junk when received that was composed in HTML and includes embedded images or objects that must be rendered from a remote server to be viewed, any such objects will not be automatically rendered as a safety feature.

As protection from spammers in case a spam message is not automatically marked as Junk when received that contains embedded images or objects that must be rendered from a remote server to be viewed, you should not automatically render all HTML received as additional protection.

What is your setting at Mail > Preferences > Viewing for "Display remote images in HTML messages"?

What type of email account - .Mac, IMAP or POP?

Since the same occurs with both email accounts, this may be a cache problem so to rule this out along with any other system problems, as a first step check Resolving Disk, Permission, and Cache Corruption for system troubleshooting procedures and when doing so, follow all steps/instructions in the order provided.

Try using the Rebuild Mailbox function on the Inbox mailbox for each account.

I find this kind of funny because I just turned off all HTML in Mail on purpose with a Terminal command.

Has anyone else been messing with your computer?

I don't have the Terminal commands to redo HTML here at the office , will have to wait until I get home, but if you trash the preferences for Mail that should fix it.

Quit Mail then go to user/Library/Preferences and delete com.apple.mail.plist

Then restart Mail and see what happens.

There is another one with the same name in /Library/Preferences that you can trash as well if that doesn't work but it's most likely your user preference. If no one was messing with your computer probably just a corrupt preference because there is no way to turn HTML off in Mail other than through a Terminal command line that changes your user preference file. You can't have done it by accident.

Me too!!!

Some months ago I noticed this problem. There is a couple of info I can add:

1. the problem happen only with MS Exchange server
2. Torn off and then on (via terminal) the html rendering, do nothing useful

So, I think it isn't related ti defect in preferences, but may be is a problem in the format of exchange html mail.
This is a very bad problem, 'cause Exchange servers are everywhere in the professional world (in this poor world...)

This is a very strange problem: I asked one of my collegues to resend the incriminated mail on another of my address (one that is not on Exchange) and the html formatting as reborn. The original sending server is still Exchange.
You say "it was definitely a prefs problem" because the server you are connected is surely not an Exchange or for other reason?

Here is how to turn HTML off. Open Terminal and paste this:

defaults write com.apple.mail PreferPlainText -bool TRUE

This is how to turn it back on again:

defaults write com.apple.mail PreferPlainText -bool FALSE

I know these work because I've tried them both. However, if your preferences file is corrupted this might not solve the problem or will just solve it temporarily. Other things are bound to go wrong.