mail-addons/mail_multi_website/views/website_views.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2018 Ivan Yelizariev <https://it-projects.info/team/yelizariev>
     License LGPL-3.0 or later (https://www.gnu.org/licenses/lgpl.html). -->
<odoo>
    <record id="view_website_multi_mail_form" model="ir.ui.view">
        <field name="model">website</field>
        <field name="inherit_id" ref="website.view_website_form"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='default_lang_id']" position="after">
                <field name="mail_server_id"/>
            </xpath>
        </field>
    </record>
</odoo>