Stylesheet email header

Is there a way to write to the emails header where you would include stylesheets references for supported clients?

It is better to use <style> tags and not stylesheets in emails. If you use a stylesheet you would have to use a full path to the style sheet including the domain like <link href="https://www.yoursite.com/css/styles.css"> and the viewer would be asked if they want to download the style sheet in some email clients before it is downloaded/used.

Are you doing the style inline or doing a style block? Are you doing the style block in the "body"

Where are you referring to? I usually do inline styles for emails. Outlook is very particular in what it supports, so it is sometimes tricky.