Email marketing tool for my website

I am looking for a Email marketing tool which will use amn email template and allow user to edit its text and images and then sends it. This email marketing tool will be integrated in my website by me. The marketing tool should work independently where users will be able to change images in the template (by uploading a new one ?) edit all the texts in the template and then let user see a preview of it. The tool should support multiple templates and freelancer will have to provide me details about integrating other templates into the tool as well. I like giving a chance to new freelancers but they will have to give me a demo of a similar tool which I can test on your server.