Open Outlook and go to the Sent Items folder
Double-click the email you want to unsend
Click File
Click Info
Click Resend or Recall
Click Recall This Message
Choose Delete unread copies of this message or Delete unread copies and replace with a new message
Select Tell me if recall succeeds or fails for each recipient if needed
Click OK
Note that recall only works in some Microsoft Exchange or Microsoft 365 accounts
Note that recall usually does not work for emails sent to external recipients
Use Undo Send in Outlook on the web or Outlook desktop if the option is available
Set the Undo Send delay in Outlook settings before sending future emails