[theshadowmonkey]

I worked on a transactional email infrastructure where we used to send 50k-100k emails at a time and a few million a day. We used inky and juice to customize email generation and caching partial templates using inky worked out well at scale. Only problem was with all the fallbacks, some emails used to get large enough and gmail used to clip them at the bottom. https://get.foundation/emails/docs/inky.html

Not sure if the framework is as advanced. But, seems to solve a lot of basic issues. Surprising that providers like sparkpost or ses are not able to solve generation at scale problem with templates.