If you selected the MJML option when you exported your emails from the Emailify plugin, your exported email folder(s) will include an additional index.mjml alongside the regular HTML file.

Having the MJML file makes it really easy for a developer to open up the file in their code editor and make any manual updates or customisations, without needing to deal with the compiled HTML tables that are much harder to work with.

Once the updates have been made, they can be compiled into HTML by using one of a number of methods detailed in the usage section on the MJML documentation site.