Found this on a website:
"If you are using MS outlook, you can recall an email message.
Next time you do such boo boos, go to your sent items immediately and double click on the message. Now go to ACTIONS - Recall This Message.
I have never used this feature before so I'm not sure what exactly happens. But I heard that this won't work if the other party has already downloaded the message from their email server.
Also, a notification goes to the recipient saying the email sent by you has been recalled. So you still owe the recipient an explanation ;) "
Good luck. If you are not in Outlook, then you can probably apologise sincerely to him. Most people understand that even your best friend sometimes gets frustrated with you. How does the saying go? "If you knew what your friends sometimes said about you, you wouldn't have any friends".