I hand code all of my company's emails in HTML. Last week, I wanted to insert some dynamic content that I had created (using segments and snippets) into my HTML, I was surprised to learn that the only way you can insert dynamic content into your email is if you are using the WYSIWYG editor. Every other email service provider I have ever used has always provided a little piece of code to insert into your HTML code that references the dynamic content, much like how Marketo's tokens work {{here is a token I could place into my HTML}}.