HTML email with Jinja

Layout of a campaign

Keep copy and layout apart: one folder per campaign holding template.html and a data file (config.json or YAML) with the subject, preheader, body copy and product rows.
Shared header and footer go in partials ({% include 'partials/header.html' %}). Never paste copies into each template.
If data keys and template variable names differ, do the mapping in one function. Adding a copy field means updating that function, or the template renders nothing for it. When you rename a key, translate the old name on load so old campaigns keep rendering.
Prefer lists and loops ({% for p in products %}) over numbered variables (Product1_Name, Product2_Name, ...).

Email clients are not browsers. These rules are not optional: