Source: Sample E-mail To Convert
This is not an email. It is only HTML markup.
Here is a link to my jsfiddle content.
This is an email. Do you need to do this via JS? Is it possible, for example, to parse the email server-side and send JSON to the browser? That would be the simplest, most robust approach.
Do you need to be able to handle multi-part emails? If not, you might be able to split the email into header / body (split on the blank line), and then split the header into individual lines (split on newline) so you can read each name:value (split on colon).
Displaying the body as HTML is risky, since it would allow for code injection. Not sure how to approach that from the client side.
All this is fairly complex, though. There are server-side tools and libraries that could handle it much easier, and much more reliably. Plus, it would be a small fraction of the work.
