Email reminders are sent out by a service called Nudgemail. Their service is secure and they won't sell or share your email address with 3rd parties. They will not send you unsolicited emails either and require no sign up to use.
Simply click the "Remind Me" button next to the closing date on each contest and as long as your web browser is setup correctly it will open your email client and the email will already be setup for you. Simply click send and you will receive the email back 3 days before the closing date of the remix contest. This is a nice handy reminder to get your remix entries in or to hurry up and get that remix finished in time.
If you want to turn off all email reminders simply send an email from the same email address to [email protected].