The immediate delivery of e-mail has consequences. Once you have sent an e-mail, you may not be able to take it back. This can cause problems if you send a message when you are not ready to do this – or send it to the wrong people. The good news is that Gmail offers a fast, effective way to send or retrieve an email before the worst happens. This returns the e-mail and prevents it from appearing in someone's inbox until you are done. Here's how to use the feature on both mobile and internet.
Step 1: Check your unsent settings
In the past you had to enable the option Not sent to call up Gmail emails. However, Google has made this a standard feature for Gmail, so it's now always enabled. But you still need to check the settings to make sure that they have been adjusted correctly.
Start by signing in to Gmail. Then select the gear icon in the top right corner, just above your email list. Select Settings in this menu.
Step 2: Adjust settings if necessary
The settings menu contains all special functions that you can activate or adjust in Gmail. Scroll down on the General tab until you see the Undo Send section. Here you see an option to adjust the cancellation period . You can choose how long you need to be able to display an e-mail. You can choose from a maximum of five, 1
If you are concerned about sending the wrong email, you probably want to set the cancellation period to at least 10 seconds, just to be sure. Five seconds is not very long to realize that you made a mistake and clicked on the unsent option. When you are finished, browse to the bottom of the Settings section and save your changes.
Please note that the email can be displayed in the inboxes of those to whom you have sent it while the unsent option is present. When you call up the e-mail, it disappears, but it is possible that someone started reading it, so it is still important to act quickly.
Step 3: Send a test e-mail
Now that you know how long you have to remember an e-mail, it's time to test the service. Press Compose and send a quick e-mail to yourself. When you are finished, press the blue button Send .
Now immediately look in the bottom left corner of your Gmail window. You should see a quickly sent message there that says Message sent . In the middle of the notification bar there is an option for Undo .
If you wait, you will see the option Undo which means that your cancellation period has expired and it is now too late to retrieve the e-mail. If you are not sure how long you need to set your cancellation period, we recommend you try this a few times to get an idea of how long different periods are.
Press the option Undo and you will see that your e-mail reappears in the same state in which you sent it. This allows you to freely change or address the content before sending it as intended. Once the email has been retrieved, there is no time limit for how long to work on it – or you can simply delete it and start over.
You may also want to view other tips and tricks for Gmail here.  Calling up an email on iOS or Android
Calling up an email on iOS or Android is as easy as in the web browser and requires no tweak settings or options. After you send an email, you'll see the option to undo at the bottom of the screen (although on the right, instead of on the left). Press that button and you should be good to go. Keep in mind that the button will only be displayed for a few seconds, so be quick.
As with the web client, we recommend sending a test email to see if this feature works for your account before you trust it.