$tableauUser = [
    ["username"=>"Zoukilama", "email"=>"zouki.dev@gmail.com", "grade"=>"superadmin"],
    ["username"=>"Neated", "email"=>"neated@gmail.fr", "grade"=>"user"],
    ["username"=>"Marcel", "email"=>"marcel@hotmail.fr", "grade"=>"user"],
    ["username"=>"Mélanie", "email"=>"mela@hotmail.fr", "grade"=>"user"],
    ["username"=>"Kevin", "email"=>"kevin-xx-big-bos@hotmail.fr", "grade"=>"user"]
];
$data = "";
foreach($tableauUser as $value){
    $data .= $value['username'].': <b>'.$value['email'].'</b> ';

    if($value['grade'] == "user") {
        $data .= 'Grade: <b>Utilisateur</b><br/>';
    } else if ($value['grade'] == "superadmin") {
        $data .= 'Grade: <b>Administreur</b><br/>';
    }
}
echo $data;