social/mass_mailing_keep_archives/mass_mailing_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record id="view_mail_mass_mailing_form" model="ir.ui.view">
            <field name="name">mail.mass_mailing.keep_archives.form</field>
            <field name="model">mail.mass_mailing</field>
            <field name="inherit_id" ref="mass_mailing.view_mail_mass_mailing_form"/>
            <field name="arch" type="xml">
                <label for="reply_to" position="before">
                    <field name="keep_archives"/>
                </label>
            </field>
        </record>
    </data>
</openerp>