settings.php

<?php

defined('MOODLE_INTERNAL') || die;

if($ADMIN->fulltree) {
    $select = array(0 => get_string('no'), 1 => get_string('yes'));
    $settings->add(new admin_setting_configselect('block_quickmail_allowstudents',
        get_string('allowstudents', 'block_quickmail'), get_string('allowstudents',
        'block_quickmail'), 0, $select));

    $roles = $DB->get_records_menu('role', null, 'sortorder ASC', 'id, name');
    $defaults = array_map(function ($sn) use ($DB) {
        return $DB->get_field('role', 'id', array('shortname' => $sn));
    }, array('editingteacher', 'teacher', 'student'));
    $settings->add(new admin_setting_configmultiselect('block_quickmail_roleselection',
        get_string('select_roles', 'block_quickmail'), get_string('select_roles',
        'block_quickmail'), $defaults, $roles));
}