social/mail_print/report.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>

        <report
                id="mail_message_pdf"
                model="mail.message"
                string="Email"
                report_type="qweb-pdf"
                name="mail_print.mail_message"
                file="mail_print.mail_message"
        />

    </data>
</openerp>