Gmail has the function to recall a message after you sent it out. Once in a while, you may make errors and need to recall a message after sending it out. In Gmail, you have 20 seconds by default to recall a sent message, however, you can change to a different number, e.g., 30 seconds or 10 seconds. Please see below how to recall a message.
Step 1: Log in your Gmail account (please refer here to open one if you do not have an account yet);
Step 2: In the Gmail account, click the "Compose" button from the folder list on the left;
Step 3: Draft your email in the message window and click the "Send" button at the bottom;
Step 4: You will see a bar at the left-bottom in the current window with the message: "Message sent, Undo, and View message";
Step 5: Click the "Undo" button, you will recall your message and the bar changes to "Sending undone".