[FIX] mass_mailing: bounced statistics

A mass mailing can be considered both as bounced and opened. This can
occur with some email providers, such as Gmail. Indeed, Gmail sends
out-of-office replies to the `Return-Path` address, which is also used
for bounced emails. Therefore, it is not possible to determine
accurately if a message sent to to the `Return-Path` is a genuine
bounced email, or an out-of-office reply.

However, if the recipient opens the email, it is possible to determine
that the bounce was counted incorrectly. In this case, we empty the
`bounced` field. Similarly, we only write on the `bounced` filed if the
`opened` field is empty. This could occur if the recipient opens the
email before the out-of-office reply is received.

As a bonus, we also make sure to avoid updating the status if no route
was found. No route means that the email was bounced, so no reason to
set it as opened.

opw-1869957

addons/mass_mailing/models/mail_thread.py

@@ -35,7 +35,7 @@ class MailThread(models.AbstractModel):
         """ Override to update the parent mail statistics. The parent is found
         by using the References header of the incoming message and looking for
         matching message_id in mail.mail.statistics. """
-        if message.get('References'):
+        if message.get('References') and routes:
             message_ids = [x.strip() for x in decode_smtp_header(message['References']).split()]
             self.env['mail.mail.statistics'].set_opened(mail_message_ids=message_ids)
             self.env['mail.mail.statistics'].set_replied(mail_message_ids=message_ids)

addons/mass_mailing/models/mass_mailing_stats.py

@@ -106,7 +106,7 @@ class MailMailStats(models.Model):
 
     def set_opened(self, mail_mail_ids=None, mail_message_ids=None):
         statistics = self._get_records(mail_mail_ids, mail_message_ids, [('opened', '=', False)])
-        statistics.write({'opened': fields.Datetime.now()})
+        statistics.write({'opened': fields.Datetime.now(), 'bounced': False})
         return statistics
 
     def set_clicked(self, mail_mail_ids=None, mail_message_ids=None):
@@ -120,6 +120,7 @@ class MailMailStats(models.Model):
         return statistics
 
     def set_bounced(self, mail_mail_ids=None, mail_message_ids=None):
-        statistics = self._get_records(mail_mail_ids, mail_message_ids, [('bounced', '=', False)])
+        statistics = self._get_records(
+            mail_mail_ids, mail_message_ids, [('bounced', '=', False), ('opened', '=', False)])
         statistics.write({'bounced': fields.Datetime.now()})
         return statistics