The current template input page shows this text:
You can use these variables in the templates. $hyperkitty_url: Permalink to archived message in Hyperkitty $listname: Name of the Mailing List e.g. ant@example.com $list_id: The List-ID header e.g. ant.example.com $display_name: Display name of the mailing list e.g. Ant $short_listname: Local part of the listname e.g. ant $domain: The domain part of the listname e.g. example.com $info: The mailing list's longer descriptive text $request_email: The email address for -request address $owner_email: The email address for -owner address $site_email: The email address to reach the owners of the site $language: The two letter language code for list's preferred language e.g. fr, en, de
I suggest to add the variable for leaving a mailing list here. But what is the variable name?