Generally, we don’t believe email copy belongs in your code base.
You can upload MJML if you’d really like to, along with designing in Figma via an integration, but really your best bet is our editor.
We've extended MJML to support additional platforms and it's lightning fast to just send an email.
If we can save a few engineering hours just by having the product person who needs to update the emails with new copy actually update the copy instead of pinging engineering, we think we’ve improved things.
We also support product and marketing email, along with transactional emails.