The "Undo Send" option has been tested by Google's Gmail since 2009. Unless a user activated the feature in the Labs section of Gmail, they did not have access to it, according to Venture Beat.

Now, Google is making this an official feature for the Web version of Gmail. Until now, most users were not able to change their mind on sending an email.

Google has been testing the "Undo Send" option and other new features in the Labs section of Gmail. Users had to go in and manually activate this feature if they wanted to use it.

The "Undo Send" feature will give users a certain amount of time after they send an email to change their mind. After the email has been sent, users will have between five and 30 seconds to undo the sending of the email.

In the near future, the "Undo Send" option will appear in the "General" tab of Gmail's settings. If users already had the option turned on through the Labs section, it will still be on by default. If they did not already have turned on, they will have to check the box labeled "Enable Undo Send."

The "Undo Send" option gives users the opportunity to quickly change their mind about something they just sent. For instance, an email meant for a spouse is accidentally addressed to a boss. With the "Undo Send" option a user will have up to 30 seconds to get that email back and properly address it.

According to The New York Times, there is also an undo feature available on the mobile version of Gmail. 

Users can find the "Undo Send" option by clicking the gear in the upper right hand corner of Gmail. They then will click "Settings." The first tab that will appear is the "General" tab. The "Undo Send" option can be found by scrolling down about halfway.