PHP - update - no cambia la contraseña

<?php

    if(isset($_POST['nuevaclave'])){

        $lanewclavelink = mysqli_query($conexion, "SELECT * FROM sendes WHERE email = '".$_GET['email']."' AND codenr = '".$_GET['key']."'")or die(mysqli_error());

        $nuevaclave = utf8_decode(mysqli_real_escape_string($conexion, $_POST['password']));

        $nuevaclave2 = utf8_decode(mysqli_real_escape_string($conexion, $_POST['repassword']));

        $encrip = md5($nuevaclave);

        $preguntasegura = "Sends";

        if($_POST['password'] == '' or $_POST['repassword'] == '' or $_POST['preguntasegura'] == ''){

            echo "Lo sentimos pero no puede quedar ningún campo en blanco.";

        }

        else if($_POST['preguntasegura'] != $preguntasegura){

            echo "Lo sentimos pero has escrito mal la pregunta de seguridad. Escriba: Sends";

        }

        else{

            $duda = mysqli_fetch_assoc($lanewclavelink);

            $ya = mysqli_query($conexion, "UPDATE sendes SET password = '".$encrip."' WHERE email = '".$email."'")or die(mysqli_error());

            echo "Guardado correctamente. Ya dispones de tu nueva contraseña para acceder a Sends.";

        }

    }

    ?>

$ya = mysqli_query($conexion, "UPDATE sendes SET password = '".$nuevaclave."' WHERE email = '".$email."'")or die(mysqli_error());

Notice: Undefined variable: email in C:\myxampp\htdocs\9e05b4e4ac8darestor2ad4feb6823938e3ac4\index.php on line 52

$email = $_GET['email'];

$selecg = mysqli_query($conexion, "SELECT codenr FROM sendes")or die(mysqli_error());

while($codey = mysqli_fetch_assoc($selecg)){

    if($codey['codenr'] != $_GET['key']){

        echo "Error";

    }

    else{

        echo "aqui todo el html lo que se tiene que mostrar";

    }

}

?email=tomaselbrujo@hotmail.com&key=1693baeb16bda1dcf84f8fe28e11ee495

&key=1693baeb16bda1dcf84f8fe28e11ee495

?email=tomaselbrujo@hotmail.com

Notice: Undefined index: key in C:\myxampp\htdocs\9e05b4e4ac8darestor2ad4feb6823938e3ac4\index.php on line 7

$selecg = mysqli_query($conexion, "SELECT codenr FROM sendes")or die(mysqli_error());

$debugg = mysqli_fetch_assoc($selecg);

$de1 = mysqli_query($conexion, "SELECT * FROM sendes WHERE email = '".$_GET['email']."'")or die(mysqli_error());

$de2 = mysqli_query($conexion, "SELECT * FROM sendes WHERE codenr = '".$_GET['key']."'")or die(mysqli_error());