diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index 98349aa5308..5e606a5c473 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -861,7 +861,11 @@ class MailThread(models.AbstractModel):
 
         # compute references to find if message is a reply to an existing thread
         thread_references = message_dict['references'] or message_dict['in_reply_to']
-        msg_references = [ref for ref in tools.mail_header_msgid_re.findall(thread_references) if 'reply_to' not in ref]
+        msg_references = [
+            re.sub(r'[\r\n\t ]+', r'', ref)  # "Unfold" buggy references
+            for ref in tools.mail_header_msgid_re.findall(thread_references)
+            if 'reply_to' not in ref
+        ]
         mail_messages = self.env['mail.message'].sudo().search([('message_id', 'in', msg_references)], limit=1, order='id desc, message_id')
         is_a_reply = bool(mail_messages)
         reply_model, reply_thread_id = mail_messages.model, mail_messages.res_id
diff --git a/addons/test_mail/tests/test_mail_gateway.py b/addons/test_mail/tests/test_mail_gateway.py
index f7969cc1ac6..35597ee1299 100644
--- a/addons/test_mail/tests/test_mail_gateway.py
+++ b/addons/test_mail/tests/test_mail_gateway.py
@@ -931,6 +931,27 @@ class TestMailgateway(TestMailCommon):
         self.assertEqual(len(self.test_record.message_ids), init_msg_count + 1)
         self.assertEqual(self.fake_email.child_ids, self.test_record.message_ids[0])
 
+    @mute_logger('odoo.addons.mail.models.mail_thread')
+    def test_message_process_references_external_buggy_message_id(self):
+        """
+        Incoming email being a reply to an external email processed by
+        odoo should update thread accordingly. Special case when the
+        external mail service wrongly folds the message_id on several
+        lines.
+        """
+        new_message_id = '<ThisIsTooMuchFake.MonsterEmail.789@agrolait.com>'
+        buggy_message_id = new_message_id.replace('MonsterEmail', 'Monster\r\n  Email')
+        self.fake_email.write({
+            'message_id': new_message_id
+        })
+        init_msg_count = len(self.test_record.message_ids)
+        self.format_and_process(
+            MAIL_TEMPLATE, self.email_from, 'erroneous@test.com',
+            extra='References: <2233@a.com>\r\n\t<3edss_dsa@b.com> %s' % buggy_message_id)
+
+        self.assertEqual(len(self.test_record.message_ids), init_msg_count + 1)
+        self.assertEqual(self.fake_email.child_ids, self.test_record.message_ids[0])
+
     @mute_logger('odoo.addons.mail.models.mail_thread')
     def test_message_process_references_forward(self):
         """ Incoming email using references but with alias forward should not go into references destination """
diff --git a/doc/cla/individual/veryberry.md b/doc/cla/individual/veryberry.md
new file mode 100644
index 00000000000..b923b1f2c29
--- /dev/null
+++ b/doc/cla/individual/veryberry.md
@@ -0,0 +1,11 @@
+Belarus, 2021-03-16
+
+I hereby agree to the terms of the Odoo Individual Contributor License
+Agreement v1.0.
+
+I declare that I am authorized and able to make this agreement and sign this
+declaration.
+
+Signed,
+
+Veronika Kotovich veronika.kotovich@gmail.com https://github.com/veryberry