Use Mandrill API/SMTP compatibility mode by checking "Email Only To:?" in Downloads > Settings > Emails.
Alternately, add the following to your theme's `functions.php` file.
function my_eddsr_get_email_to( $to, $payment_id ) {
$to = edd_get_payment_user_email( $payment_id );
return $to;
}
add_filter( 'eddsr_get_email_to', 'my_eddsr_get_email_to', 10, 2 );