diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index fea2017f40c..0f77a14a5f1 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -1862,10 +1862,8 @@ class MailThread(models.AbstractModel):
         # _mail_flat_thread: automatically set free messages to the first posted message
         MailMessage = self.env['mail.message']
         if self._mail_flat_thread and model and not parent_id and self.ids:
-            messages = MailMessage.search(['&', ('res_id', '=', self.ids[0]), ('model', '=', model), ('message_type', '=', 'email')], order="id ASC", limit=1)
-            if not messages:
-                messages = MailMessage.search(['&', ('res_id', '=', self.ids[0]), ('model', '=', model)], order="id ASC", limit=1)
-            parent_id = messages and messages[0].id or False
+            messages = MailMessage.search(['&', ('res_id', '=', self.ids[0]), ('model', '=', model)], order="id ASC", limit=1)
+            parent_id = messages.ids and messages.ids[0] or False
         # we want to set a parent: force to set the parent_id to the oldest ancestor, to avoid having more than 1 level of thread
         elif parent_id:
             messages = MailMessage.sudo().search([('id', '=', parent_id), ('parent_id', '!=', False)], limit=1)
diff --git a/addons/test_mail/tests/test_performance.py b/addons/test_mail/tests/test_performance.py
index 20236364df9..eeef3e2519d 100644
--- a/addons/test_mail/tests/test_performance.py
+++ b/addons/test_mail/tests/test_performance.py
@@ -243,7 +243,7 @@ class TestHeavyMailPerformance(TransactionCase):
         self.umbrella.message_subscribe(self.user_portal.partner_id.ids)
         record = self.umbrella.sudo(self.env.user)
 
-        with self.assertQueryCount(admin=124, emp=157):  # com runbot 122 - 155 // test_mail only: 118 - 150
+        with self.assertQueryCount(admin=123, emp=156):  # com runbot 121 - 154 // test_mail only: 117 - 149
             record.message_post(
                 body='<p>Test Post Performances</p>',
                 message_type='comment',
@@ -260,7 +260,7 @@ class TestHeavyMailPerformance(TransactionCase):
         record = self.umbrella.sudo(self.env.user)
         template_id = self.env.ref('test_mail.mail_test_tpl').id
 
-        with self.assertQueryCount(admin=149, emp=197):  # com runbot 147 - 195 // test_mail only: 141 - 187
+        with self.assertQueryCount(admin=148, emp=196):  # com runbot 146 - 194 // test_mail only: 140 - 186
             record.message_post_with_template(template_id, message_type='comment', composition_mode='comment')
 
         self.assertEqual(record.message_ids[0].body, '<p>Adding stuff on %s</p>' % record.name)
@@ -276,7 +276,7 @@ class TestHeavyMailPerformance(TransactionCase):
         customer_id = self.customer.id
         user_id = self.user_portal.id
 
-        with self.assertQueryCount(admin=336, emp=398):  # test_mail only: 323 - 383
+        with self.assertQueryCount(admin=335, emp=397):  # test_mail only: 322 - 382
             rec = self.env['mail.test.full'].create({
                 'name': 'Test',
                 'umbrella_id': umbrella_id,
@@ -315,7 +315,7 @@ class TestHeavyMailPerformance(TransactionCase):
         })
         self.assertEqual(rec.message_partner_ids, self.user_portal.partner_id | self.env.user.partner_id)
 
-        with self.assertQueryCount(admin=239, emp=279):  # test_mail only: 233 - 271
+        with self.assertQueryCount(admin=238, emp=278):  # test_mail only: 231 - 270
             rec.write({
                 'name': 'Test2',
                 'umbrella_id': umbrella_id,