Even when using mjml you must do render tests of your templates using litmus or a similar service. Mjml is WAY better than hand rolling templates but there are foot guns to be found and the docs won’t mention most of them https://github.com/mjmlio/mjml/issues/2927#issuecomment-2539....
replyTotally agree on edge case quirks of MJML - or more like weird behaviors in Outlook. With so many email services and clients around, nothing can provide 100% bulletproof solution but I think MJML is as close as it gets to works-for-majority. I‘m sure MJML maintainers also aim for this.
replyAlso, yes! Microsoft should kill Outlook with fire! :)