When setting up an Email Campaign you can schedule it for a specific date and time in the future. Once you press confirm campaign, you campaign will go into queue (it will not be sent until the specified date and time).
If you decide that you want to change something in your campaign, you can stop it from being sent by clicking the “Delete” button in the Sent Campaigns Report.
Unfortunately if you campaign has already been sent, there is no way to recall your email.