Allow an image to be used as the background of a newsletter.
In our office, the background of all of our documents is an image. I cannot recreate this style in the newsletter as I can only select a block colour - Having a box that allows you to select an image from your computer and have it used as the background would be great for us and I'm sure other offices will benefit.
Not technically possible to implement.
This is a deliberate omission.
HTML emails seem similar to websites on the surface but are a bit of an ancient and complex beast - they support a small subset of what is actually available on the web.
All the email clients (e.g. Hotmail, Outlook etc.) support a slightly different subset of features. The toolset and settings provided in the Rex newsletter builder match the lowest common denominator which should guarantee a similar appearance of your newsletters regardless of what email client they're being viewed in (e.g. gmail, outlook.com, outlook 2003/07/10/13, outlook on mac, Thunderbird, Yahoo.com, Apple mail, iOS, android etc.)
Background images unfortunately aren't supported by Outlook email clients hence their omission.
A great resource for this generally can be found here: https://www.campaignmonitor.com/resources/will-it-work/ or more specifically in regards to background images here: https://www.campaignmonitor.com/css/ (see the background part).