Open Outlook
Go to the Sent Items folder
Double-click the email you want to cancel
Select Message
Select Actions
Click Recall This Message
Choose Delete unread copies of this message or Delete unread copies and replace with a new message
Select whether to tell you if the recall succeeds or fails for each recipient
Click OK
If prompted, confirm the action
Note that recall works only if the recipient uses Outlook in the same organization and has not read the email