Why not just use Majordomo? It probably does what you want already, and if not, it's highly configurable, and as a bonus, it is written in Perl so that you can customize it however you see fit. It is tried and proven.

To answer your second question, yes, it's possible to send messages with a plain text component and an HTML component. Many popular mail readers will know what to do with it (hint, you use MIME types).