odoo/addons/mail/data/mail_group_data.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data noupdate="1">

        <record model="mail.group" id="group_sales">
            <field name="name">Sales</field>
            <field name="description">Discussion about best sales practices and deals.</field>
        </record>
        <record model="mail.group" id="group_all_employees">
            <field name="name">All Employees</field>
            <field name="group_ids" eval="[(4, ref('base.group_user'))]"/>
            <field name="description">Discussion about best sales practices and deals.</field>
        </record>

        <!-- notify all employees of module installation -->
        <function model="mail.group" name="message_post">
            <!-- thread_id, body='', subject=False, msg_type='notification', parent_id=False -->
            <value eval="[ref('mail.group_all_employees')]"/>
            <value>Your homepage is a summary of messages you received and key information about documents you follow.

The top menu bar contains all applications you installed. You can use this &lt;i&gt;Settings&lt;/i&gt; menu to install more applications, activate others features or give access to new users.

To setup your preferences (name, email signature, avatar), click on the top right corner.</value>
            <value>Welcome to OpenERP!</value>
        </function>

    </data>
</openerp>