(Asking for someone I’ve been mentoring.)

TLDR; Looking for recommended resources on how to code email templates from scratch.

I’ve been helping a friend transition their career from sales to web development and recently he applied for a position as a jr developer for an ecommerce startup. They liked him and they’re willing to create a new position for him where he’ll work with both the marketing department and the development team. He’ll start with building email templates for the marketing department and eventually move on to development as he grows his skills. I’d really appreciate it if I could get some recommended resources for learning how to code email templates from scratch and from PSDs. This would be a life changer for him and I’m trying to do as much as I can to help me out.