How many times have you sent an email to the wrong person, and then every cell in your body wished – what if you could just make it stop? I have been through this a few times, and it could have been worst blunders ever. And to save you from that blunder, two years ago, Google rolled out an ‘Undo send’ feature on Gmail.  As the name suggests, it lets you undo your blunder email. Though an old feature, a lot of people are still unaware of its existence, and some are unsure how to enable it. And so, in this article we will tell you how this feature really works, and take you through a step-by-step process of enabling it.
To begin with, it is important to understand that the undo feature, essentially gives a user a buffer time of 5-30 seconds (depending on the settings) to retrieve a sent email. Post the chosen time, the email cannot be undone or retrieved. If you are wondering why your Gmail does not show the feature, even when it has been around for two years, it’s because you need the enable it in Gmail settings. Here’s how to go about it.
To begin with, you need to sign in to your Gmail account. Now, on the top right corner, click on the ‘gear’ icon, and from the drop-down list choose ‘Settings’. 
gmail-settings
From there, scroll down a little till you spot the ‘Undo Send’ option. Here, check the box next to it to enable the feature, and select the ‘Send cancellation period’, which is essentially the time bracket you have at hand to retrieve your email before it is permanently sent.
undo-send-gmail
gamil-undo-email
Scroll down a bit more and save your changes. And done! Your undo feature is now enabled.
After you have enabled the feature, each time you send an email, right on top of your inbox, you will see a pop-up notification, which will give you an option to either undo or view your message. The notification will show up for a few seconds, depending on the time chosen in the settings post which, the email will be sent permanently. Within that time, if you tap on unsend, the email will immediately be retrieved, and your compose box will reopen. 
demao-gmail-email
gmail-email-demo-2
gmail-email-demo-3
Do note, when you enable the ‘undo send’ feature, the time taken for the email to be delivered will also be delayed by the amount of buffer time you choose. 
{BGR}