* Activate access to **Technical Features** (debug mode).
* Go to **Settings > Technical > Email > Subject Replacement Templates**
* Create a new template.

    * The field **Model** specifies the model to which the subject template should apply in the notification emails sent by Odoo.
    * The field **Subject Template** accepts `Jinja <https://jinja.palletsprojects.com/en/2.11.x/>`__ expressions.
    * The field **Replace** specifies if the template should replace existing content or append to it.