flectra/addons/mass_mailing/security/mass_mailing_security.xml

<?xml version="1.0" encoding="utf-8"?>
<flectra>
    <record id="group_mass_mailing_user" model="res.groups">
        <field name="name">User</field>
        <field name="category_id" ref="base.module_category_mass_mailing"/>
        <field name="users" eval="[(4, ref('base.user_root'))]"/>
        <field name="implied_ids" eval="[(4, ref('base.group_user'))]"/>
    </record>

    <!-- Group to manage campaigns -->
    <record id="group_mass_mailing_campaign" model="res.groups">
        <field name="name">Manage Mass Mailing Campaigns</field>
        <field name="category_id" ref="base.module_category_hidden"/>
    </record>

    <data noupdate="1">
        <record id="base.default_user" model="res.users">
            <field name="groups_id" eval="[(4,ref('mass_mailing.group_mass_mailing_user'))]"/>
        </record>
    </data>
</flectra>