mail-addons/mail_all/views/templates.xml

<?xml version="1.0" ?>
<!--# Copyright 2016 Ivan Yelizariev <https://it-projects.info/team/yelizariev>
    # Copyright 2018 Artyom Losev <https://it-projects.info/team/ArtyomLosev>
    # Copyright 2018 Kolushov Alexandr <https://it-projects.info/team/KolushovAlexandr>
    # License MIT (https://opensource.org/licenses/MIT). -->
<odoo>
        <template
        id="mail_all_assets_backend"
        name="mail_all_assets_backend"
        inherit_id="web.assets_backend"
    >
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/mail_all/static/src/css/mail_all.css" />
                <script
                src="/mail_all/static/src/js/mail_all.js"
                type="text/javascript"
            />
                <script
                src="/mail_all/static/src/js/test_mail_all.js"
                type="text/javascript"
            />
            </xpath>
        </template>
</odoo>