In the folder pane on the left of the Outlook window, choose the Sent Items folder. Open the message that you want to recall. You must double-click to open the message. Selecting the message so it appears in the reading pane won't allow you to recall the message. From the Message tab, select Actions > Recall This Message. Click Delete unread copies of this message or Delete unread copies and replace with a new message, and then click OK. If you’re sending a replacement message, compose the message, and then click Send. To check on the recall The success of the message recall depends entirely on the recipients activities and email settings. If the person has their email program open, or has there mail setup to 'mark as read' or 'sort mail automatically upon receipt', the message recall will fail. Full details and sample scenarios are available here: https://support.office.com/en-us/article/recall-or-replace-an-email-message-that-you-sent-35027f88-d655-4554-b4f8-6c0729a723a0