So a lot of brands use images in their emails when using an ESP like Klaviyo or Mailchimp. They don’t use the built in editor, and definitely not HTML. These are all very limiting in what you can do to get it on brand.
I can send you over some examples of what I mean, but it’s petty standard for Ecommerce. In the end, I just need an image of 600px wide and up to 4000px height, with average height being 2400px.
It should be pretty straightforward to do this by using the same system you already have built. It’s simply just larger images with a bit more content.