[FIX] revert commit 196a5e861c for incorrect fix

mass_mailing_statistic_extra/models/mail_mail.py

@@ -30,4 +30,4 @@ class MailMail(models.Model):
                     'email_to': ';'.join(email_list),
                     'subject': mail.subject,
                 })
-        return mail_id
+        return mail