Source

File: wp-includes/class-pop3.php

function delete ($msgNum = "") {
        //  Flags a specified msg as deleted. The msg will not
        //  be deleted until a quit() method is called.

        if(!isset($this->FP))
        {
            $this->ERROR = "POP3 delete: " . _("No connection to server");
            return false;
        }
        if(empty($msgNum))
        {
            $this->ERROR = "POP3 delete: " . _("No msg number submitted");
            return false;
        }
        $reply = $this->send_cmd("DELE $msgNum");
        if(!$this->is_ok($reply))
        {
            $this->ERROR = "POP3 delete: " . _("Command failed ") . "[$reply]";
            return false;
        }
        return true;
    }