diff --git a/mail_post_defer/models/mail_message_schedule.py b/mail_post_defer/models/mail_message_schedule.py
index eba9a0340..1adf977b8 100644
--- a/mail_post_defer/models/mail_message_schedule.py
+++ b/mail_post_defer/models/mail_message_schedule.py
@@ -13,3 +13,14 @@ class MailMessageSchedule(models.Model):
         return super(MailMessageSchedule, _self)._send_notifications(
             default_notify_kwargs=default_notify_kwargs
         )
+
+    def _group_by_model(self):
+        """Make sure only mail.thread children are grouped with model."""
+        result = super()._group_by_model()
+        for model, records in result.copy().items():
+            # Move records without mail.thread mixin to a False key
+            if model and not hasattr(model, "_notify_thread"):
+                result.pop(model)
+                result.setdefault(False, self.browse())
+                result[False] += records
+        return result
diff --git a/mail_post_defer/models/mail_thread.py b/mail_post_defer/models/mail_thread.py
index bb657c5b2..20c7737bd 100644
--- a/mail_post_defer/models/mail_thread.py
+++ b/mail_post_defer/models/mail_thread.py
@@ -1,4 +1,4 @@
-# Copyright 2022-2023 Moduon Team S.L. <info@moduon.team>
+# Copyright 2022-2024 Moduon Team S.L. <info@moduon.team>
 # License LGPL-3.0 or later (https://www.gnu.org/licenses/lgpl).
 
 from datetime import datetime, timedelta
@@ -12,7 +12,15 @@ class MailThread(models.AbstractModel):
 
     def _notify_thread(self, message, msg_vals=False, **kwargs):
         """Defer emails by default."""
-        _self = self
+        # Remember if the author should be notified when deferring
+        kwargs.setdefault(
+            "mail_post_defer_notify_author",
+            self.env.context.get("mail_notify_author", False),
+        )
+        _self = self.with_context(
+            mail_notify_author=kwargs["mail_post_defer_notify_author"]
+        )
+        # Don't defer automatically if forcing send
         if "mail_defer_seconds" not in _self.env.context:
             force_send = _self.env.context.get("mail_notify_force_send") or kwargs.get(
                 "force_send", False
@@ -21,6 +29,7 @@ class MailThread(models.AbstractModel):
             if not force_send:
                 # If deferring message, give the user some minimal time to revert it
                 _self = _self.with_context(mail_defer_seconds=30)
+        # Apply deferring
         defer_seconds = _self.env.context.get("mail_defer_seconds")
         if defer_seconds:
             kwargs.setdefault(
diff --git a/mail_post_defer/tests/test_mail.py b/mail_post_defer/tests/test_mail.py
index 3d717feb4..84a87fd09 100644
--- a/mail_post_defer/tests/test_mail.py
+++ b/mail_post_defer/tests/test_mail.py
@@ -182,6 +182,40 @@ class MessagePostCase(MailPostDeferCommon):
                 with self.assertRaises(UserError):
                     self.partner_portal._message_update_content(msg, "", [])
 
+    def test_model_without_threading(self):
+        """When models don't inherit from mail.thread, they still work."""
+        self.partner_portal.email = "portal@example.com"
+        with self.mock_mail_gateway():
+            self.env["mail.thread"].with_context(
+                mail_notify_author=True
+            ).message_notify(
+                author_id=self.partner_employee.id,
+                body="test body",
+                model="res.country",
+                partner_ids=(self.partner_employee | self.partner_portal).ids,
+                res_id=self.ref("base.es"),
+            )
+            self.assertNoMail(self.partner_employee | self.partner_portal)
+            # One minute later, the cron sends the mail
+            with freezegun.freeze_time("2023-01-02 10:01:00"):
+                self.env["mail.message.schedule"]._send_notifications_cron()
+                self.env["mail.mail"].process_email_queue()
+                self.assertMailMail(
+                    self.partner_portal,
+                    "sent",
+                    author=self.partner_employee,
+                    content="test body",
+                )
+                self.assertMailMail(
+                    self.partner_employee,
+                    "sent",
+                    author=self.partner_employee,
+                    content="test body",
+                )
+        # Safety belt to avoid false positives in this test
+        self.assertFalse(hasattr(self.env["res.country"], "_notify_thread"))
+        self.assertTrue(hasattr(self.env["res.partner"], "_notify_thread"))
+
 
 @tagged("-at_install", "post_install")
 @freezegun.freeze_time("2023-01-02 10:00:00")