Would be cool if we could use a photo or graphic as the background for our emails. Something that would be "behind" the text. Would be a bit more branding for each property/company. Or maybe the ability to add a text box on top of a photo would be easier (I know nothing about programming).
If you're good with HTML and CSS, you could probably rig something up along those lines. You'd go to Settings > Theming > pick your theme > Change the Header of your Emails > click the Edit HTML Source < > button in the editor, and drop in appropriate code.
However, I don't recommend this, because a good many email programs don't really like fancy HTML / CSS coding in emails, or ignore it, or handle it improperly. You'd want to do a lot of experiments, and even then, you can't really test everything.
What we allow by default is more ordinary and old-fashioned and more likely to work. And when it doesn't, it looks ugly but is still readable by the guest.
Please do let the community know what you discover with your experiments!
I personally think that any kind of fancy backgrounds should be avoided at all costs, what matters most of all if readability in every way that guests might read your email (IOS phone, android phone, tablet, laptop, desktop, in the car, etc).
And I also feel that a simple text email feels more real, and that's what folks renting directly from an owner are expecting. If you make it fancier some guests will start thinking you're a property management company instead of a small (and caring) owner.