Recall an email without showing receiver the original email
When you recall an email, the receiver gets an emailing telling them that you want to recall the email, but the original is still present in their inbox at the same time. Clicking the original causes the recall to fail.
However depending on their inbox layout, the receiver could view the subject and part/most of the body of the original, and then still click the recall email, which removes the original and causes it to be successful.
I think it would be more useful for the sender if when a recall is sent, the original email is hidden from the receiver. Depending on how the receiver reacts to the recall depends on if they see the original or not. Of course it would be ideal for a recall to not give the receiver the option to view the original at all, but I'm sure there's more to that.