While you still can’t use email to do things like send private messages back and forth on Facebook, the company is making another email-based feature available to everyone today. When you receive email notifications about your friends activity — photos you’re tagged in, status updates, Wall posts, videos, etc. — you can send a comment back via email.
All you have to do is reply to the email notification, typing in your comment at the top of the message body. You don’t need to be logged in for it to work. Many organizations block Facebook in the workplace — something to do with “productivity,” we hear — so this is another way for people to stay in touch with friends, engage in flame wars, etc. in spite of their IT departments.