The overall goal is to create the modules necessary to build a highly flexible Drupal-based webmail solution, without 3rd party webmail projects, like RoundCube or whatever else, being involved...only Drupal and the mail servers.
The project is fairly new, and in the planning/alpha stages, right now. It would be awesome if there's anyone that would like to help work on these projects. I just setup a homepage for the planning/development of the project at http://mailapi.gcopenhaver.com. I setup a forum there, and we will be documenting things in books on the site as we go. As of a couple days ago, there's two of us working on this project so far.
The modules:
Mail API will provide both an abstraction layer for front-end webmail user interface modules (or whatever else people come up with that could use the API) and a hooking system for back-end modules that will communicate with mail servers.
IMAP API is a back-end module (obviously for communication with IMAP servers), which will implement the Mail API hooks.
Webmail is a front-end module that will provide a webmail interface for users to access their email accounts, and will use API from Mail API to access the mail server.