Reusable templates.

We use a Jinja-like syntax (safe, sandboxed). Variables {{ name }}, conditionals {% if ... %}, loops {% for x in list %}, filters {{ total|currency('EUR') }}, {{ date|date('Y-m-d') }}.

// Template "order_confirmation"
Subject: Order #{{ order.number }} confirmed
HTML:
  
Hi {{ customer.name }},
  
Your order #{{ order.number }} is confirmed.
  

  {% for item in order.items %}
    
{{ item.qty }}x {{ item.title }} - {{ item.price|currency('EUR') }}
  {% endfor %}
  
  
Total: {{ order.total|currency('EUR') }}

Call with: POST /v1/messages + template_id, template_vars.

Every template has a current version (the one in production) and historical versions. For A/B tests you activate two variants (A and B) with a percentage split. Delivery, open and click metrics are tracked separately per variant in the panel.