The Mail app on my Mac stopped displaying message body once the message is opened.
I can still see the message body in the message preview in each mailbox, but when I click (or double click) on a specific message, the message body is blank in the new window.
This happened to me a while ago, some time after updating to El Capitan. It affects all my email accounts on my Mac, Mail works properly on my iPhone. I don't remember changing any settings.
How to resolve it?