HTML Body File Template with Variables

Other SMTP / email libraries for JS or Python have the ability to "render" an html files and pass through variables.

ie.. pseudo code:

```
var htmlTemplate = fs.readFileSync('./views/email-welcome.html', 'utf-8')

data = {
orgName: organizationName,
orgTitle: orgTitle,
email: email,
}
var emailHTML = ejs.render(htmlTemplate, data);
_sendMailgunEmail(from, email, 'Welcome to my app!', emailHTML);
```

I know I can pass html as a string and use variable that way, but that would make a for a lot in one file. Any other suggestions or could something like this be possible as feature request?