Why can't I reply to Facebook wall posts by email?

Question

As mentioned in this answer, it is supposed to be possible to respond to Facebook wall posts via email, by replying to the notification message.

This used to work for me, but now suddenly doesn't. I've tried both my normal email client and the Gmail web interface, but the result is the same: from my end it looks like the message went through, but what I wrote doesn't appear as a comment on the Facebook post, and there is no delivery failure notification or anything like that. The notifications in question do contain the text "Reply to this email to comment on this post".

How can I troubleshoot this? Is there any non-obvious requirement to these email replies that I'm missing?

EDIT: I discovered that I can in fact reply to private messages by email, just not to wall posts.

Answer 1

You can reply to private messages originally sent to you via facebook chat/inbox via email, you can also reply to messages you receive that originated in Facebook groups via email.

In my experience, most other facebook posts and notifications that you get via email cannot be replied to via email. I expect Facebook do it this way because they don't get any page views on their site if you are interacting via email, which means they will lose out on ad impressions, so it won't make them any money.