You have to be very careful with this outside the US. If it looks like the purpose of the email is promotional rather than transactional then it will require marketing permission in many countries
@sam_sexton Hey Sam! I'm a designer at Spently, so just so you know: all it does is hook into your Shopify emails to add features to it. That means that for the majority of email templates you'd make, its simply replacing the emails (with analytics, customization, etc.) that are already being sent out by Shopify based on your customers' actions. Hope that helps!
GitHub
Invoice generator
GitHub