If you send an email to the wrong recipient, send it and spot a major mistake once you press the send button or attach the wrong file, Office 365 has a message recall function. To use this in Outlook 2016 for Windows, open your sent message, click Actions, and select Recall this message. From here, you can either “Delete unread copies of this message” or “Delete unread copies and replace with a new message.” Note this only applies to unread messages and for Outlook users within the same company domain.
If you cannot see the Actions button simply type ‘recall this message’ next to the lightbulb where it says ‘tell me what you want to do’. Remember you must have the sent message open to do this.