When possible reduce your html code weight to the bare bones minimum. Nothing too fancy. Keep it logical. After a bit of practice it’s actually easy and in my opinion often faster than MJML (For example MailJet. Don’t even get me started on Klaviyo.)
Even with minimal coding/hmtl experience you can run your code through GPT-4/Bard.
Bonus for including custom instructions such as “transactional intent”, Bayesian/heuristic filtering, coded for users with poor digital accessibility, under-served internet users, etc.
Even with the best domain domain/ip reputation without a positive engagement history specific to that user you will often land in promotions/other tab and not the primary tab for new users with a heavily weighted creative.
Remember you want to mimic “an email from Grandma” while maintaining some degree of control of visual design.
Or if that’s too complicated just keep your subject line under three words and all lowercase.