mail-addons/mass_mailing_extra/views.xml

<?xml version="1.0"?>
<openerp>
    <data>

        <record model="ir.ui.view" id="view_mail_mail_statistics_form">
            <field name="name">mail.mail.statistics.form</field>
            <field name="model">mail.mail.statistics</field>
            <field name="inherit_id" ref="mass_mailing.view_mail_mail_statistics_form"/>
            <field name="arch" type="xml">
                <xpath expr="//form" position="inside">
                    <notebook>
                        <page string="Partners">
                            <group>
                                <label for="partners" string="Partners (summary)"/>
                                <field name="partners" readonly="1" nolabel="1"/>
                                <field name="partner_id" readonly="1"/>
                            </group>
                            <label for="partner_ids"/>
                            <field name="partner_ids" readonly="1"/>
                        </page>
                    </notebook>
                </xpath>
            </field>
        </record>

        <record model="ir.ui.view" id="view_mail_mail_statistics_tree">
            <field name="name">mail.mail.statistics.tree</field>
            <field name="model">mail.mail.statistics</field>
            <field name="inherit_id" ref="mass_mailing.view_mail_mail_statistics_tree"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='mail_mail_id_int']" position="before">
                    <field name="partners"/>
                </xpath>
            </field>
        </record>

    </data>
</openerp>