diff --git a/odoo/addons/base/models/ir_mail_server.py b/odoo/addons/base/models/ir_mail_server.py
index 4eb5ee8201dc35..2058d67d313700 100644
--- a/odoo/addons/base/models/ir_mail_server.py
+++ b/odoo/addons/base/models/ir_mail_server.py
@@ -405,8 +405,7 @@ def build_email(self, email_from, email_to, subject, body, email_cc=None, email_
             else:
                 message_id = make_msgid()
         msg['Message-Id'] = message_id
-        if references:
-            msg['references'] = references
+        msg['References'] = references or message_id
         msg['Subject'] = subject
         msg['From'] = email_from
         del msg['Reply-To']