CKEditor stripping HTML tags

Greetings, all,

I have constructed an email template using custom HTML that I’d like to use in Dolibarr, however, when I past the code into the source editor of CKEditor, it strips many of the tags like <head>, <link rel=“stylesheet”…>, etc. When I switch back from source to the WYSIWYG editor, the result is nothing like it should look. Is there a way I can force CKEditor to allow all of my tags so that my custom HTML will render properly? I’d like to have my emails formatted and styled in a very specific way to match the branding and formatting of my company’s website. I have attached two files. One is how the HTML should look, the other is how CKEditor strips it down.

How the HTML should look:

How CKEditor strips the HTML: