Help with HTML email.

Hi, I just want to ask for help here in Treehouse because it's one of the most friendly community that I know :)

I had my first job interview today in a digital agency, they're looking for a Junior Web Designer and I know that I'm ready for the job (I have a huge advantage because I know a lot of topics that I learn in Treehouse like Sass, Responsive Web Design, UX, etc...). If things go well, tomorrow or maybe Thursday they're going to call me to do a knowledge test, I think that the test will be design and develop a email in HTML; I know HTML and CSS (and Photoshop, obviously), I've done simple pages in HTML & CSS but I've never done a HTML email.

Can somebody tell me how to do that? I know it's HTML but I want to know the specifications, (for example, I know that an email should be maximum 600px width) I want to be ready to do a goo job in the test; I want to know how to do things well in Photoshop and then in HTML.

Thanks for the help, If I get the job that will be my first job as a Web Designer :D All thanks to Treehouse.