The most common use of Jinja2 is in web applications, where it is used to create HTML files from template files. But I have used it outside web applications too.
Email is one of those protocols that still works. It reaches me where I am. It also has various clients and libraries that work reasonably well. And it can carry almost any kind of content (Of course, there are limitations attachment size and type, etc). I use it every day, including emailing to myself.