This morning I'll like to share with you guys "how to undo sent gmail messages" ..
So I'll want you guys to read this post carefully paying close attention to the steps below:

-First, log in to your Gmail account on your computer.

-In the upper right corner of the screen,click the Settings icon (the one that looks like a gear).

-From the Settings menu, choose the option for Settings.

-From the Settings window, make sure the General tab is selected.

-Look for the setting that says Undo Send.

-Click the check box to Enable Undo Send.

-Click the drop-box to set the Send
cancellation period, meaning the number of seconds you have to prevent the email from being sent. You can choose 5, 10, 20 or 30 seconds.

-Scroll to the bottom of the Settings screen and click the Save Changes button.

-To test the feature, click the Compose button at the upper left corner of your Gmail account page.

-Compose a message and then click the Send button.

-At the top of the screen, you'll see a message that says: "Your message has been sent. Undo. View Message."

-To prevent the message from being sent, click the Undo link.

Gmail stops the message from going out and displays it in case you wish to make any changes and then resend it. If not, you can simply close the message, and it's relegated to your Drafts folder where you can keep it or delete
it.

The Undo Send feature is a handy way to ensure that the wrong email doesn't get sent to the wrong person.