- 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.