diff --git a/addons/mail/mail_thread.py b/addons/mail/mail_thread.py
index ac4a1b8ae9c..2a5d2e2a4fd 100644
--- a/addons/mail/mail_thread.py
+++ b/addons/mail/mail_thread.py
@@ -468,6 +468,8 @@ class mail_thread(osv.AbstractModel):
         # 1. Verify if this is a reply to an existing thread
         thread_references = references or in_reply_to
         ref_match = thread_references and tools.reference_re.search(thread_references)
+        use_email_to = thread_references and tools.use_email_to_re.search(thread_references)
+
         if ref_match:
             thread_id = int(ref_match.group(1))
             model = ref_match.group(2) or model
@@ -479,7 +481,7 @@ class mail_thread(osv.AbstractModel):
                 return [(model, thread_id, custom_values, uid)]
 
         # Verify whether this is a reply to a private message
-        if in_reply_to:
+        if in_reply_to and not use_email_to:
             message_ids = self.pool.get('mail.message').search(cr, uid, [('message_id', '=', in_reply_to)], limit=1, context=context)
             if message_ids:
                 message = self.pool.get('mail.message').browse(cr, uid, message_ids[0], context=context)