Add module mass_mailing_usability

Improve module link_tracker_usability

mass_mailing_usability/mail_mail_statistics.py

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 Akretion (http://www.akretion.com)
+# @author Alexis de Lattre <alexis.delattre@akretion.com>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+
+from odoo import api, fields, models
+
+
+class MailMailStatistics(models.Model):
+    _inherit = 'mail.mail.statistics'
+
+    recipient = fields.Char(store=True)
+
+    # add invalidation for 'recipient' field
+    @api.depends('res_id', 'model')
+    def _compute_recipient(self):
+        return super(MailMailStatistics, self)._compute_recipient()