diff --git a/addons/mail/models/mail_template.py b/addons/mail/models/mail_template.py
index 200057f8449..90a8314b819 100644
--- a/addons/mail/models/mail_template.py
+++ b/addons/mail/models/mail_template.py
@@ -569,6 +569,7 @@ class MailTemplate(models.Model):
                 'name': attachment[0],
                 'datas_fname': attachment[0],
                 'datas': attachment[1],
+                'type': 'binary',
                 'res_model': 'mail.message',
                 'res_id': mail.mail_message_id.id,
             }
diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index 2084f14fda3..100107bf08b 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -1673,6 +1673,7 @@ class MailThread(models.AbstractModel):
             data_attach = {
                 'name': name,
                 'datas': base64.b64encode(str(content)),
+                'type': 'binary',
                 'datas_fname': cid or name,
                 'description': name,
                 'res_model': message_data['model'],