RAW files are, by design, plain-text only. However, it is possible to insert HTML content as well.
In the “header” section of a RAW file, add the following line:
Header <Content-Type: text/html>
You can also experiment with other formats if you know how to construct multi-part MIME formatted messages manually. This might get you started:
Header <Content-Type: multipart/alternative; boundary=”__PART_BREAK”>