Microsoft Outlook contains a recall function that can unsend emails after you send them in some limited circumstances. You can only recall a sent email if you and the recipient are both using a Microsoft Exchange Server email account and the recipient hasn't read the email yet. In most circumstances, you can't unsend an email after you've sent it. If you are using a Microsoft Exchange Server, such as on a corporate or educational network, you can try to unsend a sent email. The recipient receives a notice that you've recalled the email.
Click "Mail" in the navigation pane at the left side of the Outlook window.
Click the Sent Items folder in the navigation pane.
Open the sent email message you want to unsend by clicking its name.
Click the "Message" tab on the Ribbon at the top of the Outlook window, click the "Other Actions" button in the Actions section and click "Recall This Message" in the menu that appears.
Click the "Delete Unread Copies of This Message" option in the Recall This Message window that appears.
Click the "Tell Me if Recall Succeeds or Fails for Each Recipient" check box if you don't want to receive confirmation. The check box is enabled by default.
Click the "OK" button.
The “Recall This Message” option only appears if you’re using a Microsoft Exchange Server account. You can’t unsend the email if this option doesn’t appear in the menu.
You can see if you’re using a Microsoft Exchange Server email account by clicking “File,” “Account Settings,” “Account Settings.” This window lists all your configured email accounts; Microsoft Exchange Server email accounts are identified by “Exchange” in the Type column.