Source

File: wp-includes/class-pop3.php

function popstat () {
        //  Returns an array of 2 elements. The number of undeleted
        //  msgs in the mailbox, and the size of the mbox in octets.

        $PopArray = $this->last("array");

        if($PopArray == -1) { return false; }

        if( (!$PopArray) or (empty($PopArray)) )
        {
            return false;
        }
        return $PopArray;
    }