mail-addons/email_headers/views/ir_mail_server_views.xml

<?xml version="1.0" encoding="utf-8" ?>
<odoo>
    <!-- FORM: ir.mail.server -->
    <record id="ir_mail_server_form_email_headers" model="ir.ui.view">
        <field name="name">ir.mail_server.form.email.headers</field>
        <field name="model">ir.mail_server</field>
        <field name="inherit_id" ref="base.ir_mail_server_form" />
        <field name="arch" type="xml">
            <xpath expr="//group[last()]" position="after">
                <group name="advanced" string="Smart Headers">
                    <field name="force_email_sender" />
                    <field name="force_email_reply_to" />
                    <field name="force_email_reply_to_name" />
                    <field name="force_email_reply_to_domain" />
                    <field name="force_email_from" />
                    <field name="reply_to_method" />
                    <field name="headers_example" />
                </group>
            </xpath>
        </field>
    </record>
</odoo>