Making an error on an email, replying to all by mistake or saying something you want to take back, are no longer permanent fails. Google has added an "Undo Send" feature to its Gmail on the web.

Now if you've sent something you regret you can simply hit Undo Send and all will be right in the world once more.

Anyone with Gmail can use the feature. It can even be set to control the length of time you have before it's too late to recall the mistake.

The feature has been in the experimental stages in Gmail Labs for some time as well as Google's Inbox app, but only now is it publicly available online. So how does it work and how do you turn it on?

Essentially the Undo Send option is like undo within other programs like Word. By tapping the option it will recall the email you've sent before it reaches the recipients.

This can be set to work with either five, 10, 20 or 30 seconds delay after sending an email. So there is an upper limit. Essentially it's delaying the final sending of the email to give you a little safety net.

Once sent, a pop-up will confirm "Send" has been hit and an "Undo" option will be clickable for the length of time you have the recall option set for. Once that time is up this pop-up changes to a "Sent" message without the "Undo" option.

In testing we found the email wasn't received until after the 30-second window is up, meaning it isn't sent, received and recalled, but rather simply not sent right away.

The Undo Send feature is turned off by default so you'll need to activate it if you want that safety net there.

To turn on the Undo Send feature simply go into Settings from within Gmail. To get there click on the cog at the top right and select Settings.

Then under the General tab, about 9 rows down, you'll see the Undo Send box. Simply tick this to turn it on and select from the drop-down how long you want the cancellation period to work for. Then scroll to the bottom and select Save.

For mobile users the only way to use the Undo Send option is to download and start using Google's Inbox app, rather than the Gmail app or website, apparently.

READ: Hands-on: Inbox by Gmail, a clean email app that doubles as a to-do list