diff --git a/addons/mail/models/mail_template.py b/addons/mail/models/mail_template.py
index 710dbcb8e04..b516e6d2ca1 100644
--- a/addons/mail/models/mail_template.py
+++ b/addons/mail/models/mail_template.py
@@ -79,6 +79,15 @@ class MailTemplate(models.Model):
     # CRUD
     # ------------------------------------------------------------
 
+    @api.model_create_multi
+    def create(self, vals_list):
+        templates = super().create(vals_list)
+        # fix attachment ownership
+        for template in templates:
+            if template.attachment_ids:
+                template.attachment_ids.write({'res_model': self._name, 'res_id': template.id})
+        return templates
+
     def unlink(self):
         self.unlink_action()
         return super(MailTemplate, self).unlink()
diff --git a/addons/mass_mailing/models/mailing.py b/addons/mass_mailing/models/mailing.py
index 40414588a1f..15f981c006c 100644
--- a/addons/mass_mailing/models/mailing.py
+++ b/addons/mass_mailing/models/mailing.py
@@ -417,6 +417,12 @@ class MassMailing(models.Model):
             if mailing.ab_testing_enabled and not mailing.campaign_id
         ]
         self.env['utm.campaign'].create(campaign_vals)
+
+        # fix attachment ownership
+        for mailing in mailings:
+            if mailing.attachment_ids:
+                mailing.attachment_ids.write({'res_model': self._name, 'res_id': mailing.id})
+
         return mailings
 
     def write(self, values):