social/mail_tracking/data/tracking_data.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2016 Antonio Espinosa - <antonio.espinosa@tecnativa.com>
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html). -->
<odoo>
    <record forcecreate="True" id="decimal_tracking_timestamp" model="decimal.precision">
        <field name="name">MailTracking Timestamp</field>
        <field name="digits">6</field>
    </record>
</odoo>