Version 10.10 of Subscribe2 introduced an automated reminder email feature that sends a reminder email to unconfirmed public subscribers two days after the email is originally entered. This hook allows the duration to be change or for this feature to be turned off.

function my_reminder_interval() {
    // return the number of days before removal
    // returning 0 turns this feature off
    return 7;
}
add_filter( 's2_reminder_interval', 'my_reminder_interval' );