A rough sketch for how mjml and django-mail-builder would work

example_send_code.py

msg = build_message('email/welcome.email', {'user': request.user})
msg.send()

welcome.email

{% load mjml %}

{% block subject %}Thanks for signing up to Awesome Site!{% endblock %}
{% block to %}{{ user.email }}{% endblock %}
{% block body %}
Thanks for joining our site!

We hope you love how awesome it is!
{% endblock %}

{% comment %}

As far as I can tell, this this would work by expanding our all the django variables declared, 
*then* the contents in the mjml block would be rendered to create the compiled html.

Or does this happen before?

https://github.com/liminspace/django-mjml/blob/master/mjml/templatetags/mjml.py#L18

{% endcomment %}

{% block html %}
    {% mjml %}
        <mjml>
        <mj-body>
        <mj-container>
            <mj-section>
                <mj-column>
                    <mj-text>Thanks for joining our site! </mj-text>
                    <mj-text>We hope you love how awesome it is!</mj-text>
                </mj-column>
            </mj-section>
        </mj-container>
        </mj-body>
        </mjml>
    {% endmjml %}
{% endblock %}