This project has been restarted and reinvigorated with the release of the 2.3 trunk of DBMail. While the 2.3 trunk may be a development version and therefore not suitable for production servers, it does give me a chance to rekindle the code into something much better.
The single-instance storage of the 2.3 trunk will make listing emails quicker, as the entire email does not have to be parsed to tell if it has an attachment or not. Hopefully more logic will be moved to the database, with PHP just guiding the way.
I'm just in the planning stages of this new version right now, and have only some concept code for the pulling of the email lists. Once I finalized how I'm going to implement templating - then I can start on this in earnest again.