I have now made a Debian package for the Webkit Plugin for Claws Mail I spoke about.
It is located in my PPA. It is called claws-mail-fancy-plugin.
Instead of adding my PPA, you can just download the debian packages below (however they will not get updated, only the ones in my PPA will.
Remember, to activate the plugin, open Claws Mail and go to Configuration > Plugins. Then click Load and select fancy.so. now the plugin is activated, it will render html for you. you may also want to go into Configuration > Preferences, Plugins > Fancy and select the options you want (I checked all the boxes).