diff --git a/addons/mail/models/mail_mail.py b/addons/mail/models/mail_mail.py
index aecb32cb5ac..5d90c54c0af 100644
--- a/addons/mail/models/mail_mail.py
+++ b/addons/mail/models/mail_mail.py
@@ -222,9 +222,9 @@ class MailMail(models.Model):
                 catchall_domain = self.env['ir.config_parameter'].get_param("mail.catchall.domain")
                 if bounce_alias and catchall_domain:
                     if mail.model and mail.res_id:
-                        headers['Return-Path'] = '%s-%d-%s-%d@%s' % (bounce_alias, mail.id, mail.model, mail.res_id, catchall_domain)
+                        headers['Return-Path'] = '%s+%d-%s-%d@%s' % (bounce_alias, mail.id, mail.model, mail.res_id, catchall_domain)
                     else:
-                        headers['Return-Path'] = '%s-%d@%s' % (bounce_alias, mail.id, catchall_domain)
+                        headers['Return-Path'] = '%s+%d@%s' % (bounce_alias, mail.id, catchall_domain)
                 if mail.headers:
                     try:
                         headers.update(safe_eval(mail.headers))
diff --git a/addons/mass_mailing/models/mail_thread.py b/addons/mass_mailing/models/mail_thread.py
index 0931271509d..af5782b9360 100644
--- a/addons/mass_mailing/models/mail_thread.py
+++ b/addons/mass_mailing/models/mail_thread.py
@@ -29,7 +29,7 @@ class MailThread(models.AbstractModel):
             # Bounce regex
             # Typical form of bounce is bounce_alias-128-crm.lead-34@domain
             # group(1) = the mail ID; group(2) = the model (if any); group(3) = the record ID
-            bounce_re = re.compile("%s-(\d+)-?([\w.]+)?-?(\d+)?" % re.escape(bounce_alias), re.UNICODE)
+            bounce_re = re.compile("%s\+(\d+)-?([\w.]+)?-?(\d+)?" % re.escape(bounce_alias), re.UNICODE)
             bounce_match = bounce_re.search(email_to)
             if bounce_match:
                 bounced_model, bounced_thread_id = None, False