I switched to long headers in the view options. I now want to revert back to the default view. However, going into View -> Message -> Default Headers doesn't help.
I know this is a super old thread, but wanted to show a screen shot of how I fixed this, after staring at my computer forever trying to figure it out. Just go to Preference in Mail, go to "viewing", and then click the dropdown for "Show header detail" and select default. Simple. If only I had seen that hours ago.
I switched to long headers in the view options. I now want to revert back to the default view. However, going into View -> Message -> Default Headers doesn't help.