Simple question… how to tell which template was made with GrapeJS and which with “classic” Email editor?
You mean template or email? 
You should check what is the basis of that email. Is it “blank” or an other template. Blank will create a html email while the others might create MJML.
Is this your question?
Yes, both, but primarily i mean e-mail template. Can i do something to hide HTML templates? Currently i can only tell if a template was HTML oder MJML by opening the editor and clicking on “view source” where i have a side-by-side view if it is MJML, otherwise it’s HTML in GrapeJS Editor.
I wish there would be a selectbox in the selection view to choose between the model of template (“Show MJML”, “Show HTML”) or at least a metainformation showing it in the preview image of the template itself.