Any chance you could share some more details around how you integrated mustache with MJML? I did a project almost 3 years ago now where we used MJML and Handlebars, but I was never happy with the end result and have been thinking about going back and taking another stab.

Did MJML add any support for templating engines as part of the rendering process? That didn't seem to be an option when I did the original process so we had a 2 pass solution (MJML -> HTML w/Handlebars -> HTML).