The TextStyleAdd functions apply richtext formatting. The sendmail script step only supports plaintext emails.
You can use the GetAsCSS function which should convert the richtext formatting into CSS but it won't work unless you pair it with a plugin or webservice that allows you to send HTML formatted emails. I would recommend the 360works email plugin or the Mandrill email service. Both are pretty cheap and relatively easy to use.
Thanks Evan! I will definitely lookup 360works.
Although right now I prefer local scripting (w/o any plugins) since this is just a small test project. But your suggestions are definitely considered!