system.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <section id="sendfriend" translate="label" type="text" sortOrder="120" showInDefault="1" showInWebsite="1" showInStore="1">
            <label>Email to a Friend</label>
            <tab>catalog</tab>
            <resource>Magento_Config::sendfriend</resource>
            <group id="email" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
                <label>Email Templates</label>
                <field id="enabled" translate="label" type="select" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                    <label>Enabled</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
                <field id="template" translate="label comment" type="select" sortOrder="2" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                    <label>Select Email Template</label>
                    <comment>Email template chosen based on theme fallback when "Default" option is selected.</comment>
                    <source_model>Magento\Config\Model\Config\Source\Email\Template</source_model>
                </field>
                <field id="allow_guest" translate="label" type="select" sortOrder="3" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                    <label>Allow for Guests</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
                <field id="max_recipients" translate="label" type="text" sortOrder="4" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                    <label>Max Recipients</label>
                    <frontend_class>validate-digits</frontend_class>
                </field>
                <field id="max_per_hour" translate="label" type="text" sortOrder="5" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                    <label>Max Products Sent in 1 Hour</label>
                    <frontend_class>validate-digits</frontend_class>
                </field>
                <field id="check_by" translate="label" type="select" sortOrder="6" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                    <label>Limit Sending By</label>
                    <source_model>Magento\SendFriend\Model\Source\Checktype</source_model>
                </field>
            </group>
        </section>
    </system>
</config>