You can upload your own message content by creating a new message through the blue "Create Project" button from the Email Dashboard. Follow the wizard and choose to create your project in the Simple Editor.
As you follow the steps of the Wizard, you will be asked to select a template. If your design has a layout already defined and you don't want to use one of our templates, choose the Blank Template.
You will then reach the message editor. Here, you can load in your HTML code by switching to the HTML view. The icon to show the HTML view is labeled "Source." Click on it to switch to the HTML view.
You can then copy and paste HTML code into the editor. If you need to edit the content before you save the message, click on the "Source" button again to return to the normal editing view.