After news that the functionality appeared to be rolling out gradually to Facebook users, the social networking site has now officially announced its reply-by-email features for all comments.

"When you receive an email notification about comments, you can just click 'Reply' and start typing a comment at the top of the email", explains Facebook in a blog post.

"Then hit 'Send' from your email and your reply will automatically be added as a comment on Facebook without you having to even log in".

The move might mean more engagement for many users on the site, as it makes replying quicker and easier, but it will mean a drop in page impressions (used to calculate advertising fees) for Facebook.