This is awesome. I have been half assed building an identical product for a while now, but I just can't stand dealing with html email templates. You will definitely have me as a customer for my next project. A couple thoughts:

1. The "with" in your logo is the same color as your links. Since your links aren't underlined, it makes the "with" look like a link. You should change the color of one of them.

2. The error message when I click 'execute command' without changing my email isn't obvious enough.

3. I want to see the editor. What is the interface the marketing team will see? Maybe put the template you are going to send next to that curl box.

4. Do you have decent html and responsive templates? If so, this is a selling point on its own.