Ask HN: Software for templated emails?

A while ago I gathered email adresses to > 100 tech journalists and bloggers to pitch an iOS app. Each email needed to reference a specific article written by the journalist (relevant leads only) and a generated promo code.

Manually writing each email was off the table, and using something like MailChimp or Mailgun would have been awkward (or impossible), so I wrote Enmasse – an app that creates email compiled from text templates and JSON data.

There’s a fancy video example at https://beckman.io/enmasse

Here’s the thing: I’m planning on turning this into a web service, but I’d love to hear other ways how people deal with templating emails. Maybe a tool like exists but I just haven’t found it yet? Are there specific tools for marketers that I’m unaware of? Someone wrote an excel script...?

Thanks!