Email design is a tricky thing to do. There are many more limitations with it than there is for web design or mobile design.
Email design is pretty old school and uses tables for design. Meaning anything you design has to be contained in a square and nothing fancy an be applied to the styling. So any gradients and drop shadows are a no. Unless you were to make that area into an image.
Your font choices are also limited to web safe fonts like arial, times new roman, helvetica etc. If the design is to contain real text you will have to stick to those fonts and make sure text and image/styling do not overlap as this isn’t plausible in most email clients.