Decimail Webmail's key design aim is to present a highly responsive interface to the user: although it's a webmail application, it aims to achieve comparable responsiveness to a native email program.
On the server, a simple proxy program wraps the IMAP and SMTP email communication in the HTTP protocol for communication to the browser.
Currently Decimail Webmail is tested only on Firefox 1.5 and Iceweasel 2.0; in the longer term, support for IE7, Opera and Safari should be possible. Support for IE6 would need more work but could be done; let's see how quickly IE7 takes off.
On the server side, any IMAP and SMTP server that complies with the spec should work. So far it has been tested thoroughly with Decimail Server and a little with Dovecot. It has been reported to work with Courier-imap. A web server that can proxy requests to the IMAP/SMTP proxy is needed; Apache2 has been tested. The proxy itself is written in C++ and is developed on Debian GNU/Linux, though it should be possible to run it on most POSIX systems.
Feedback about your success, or otherwise, with other environments would be most welcome.
I'm now able to use Decimail Webmail as my main email application. However it is still Alpha code and many features are missing, partially implemented or buggy. Development is progressing quickly though. It may progress more quickly if you help! The code is available at this time in the hope that potential users will take an interest and help with development, or make suggestions. If you're looking for a stable webmail application that can be deployed today in a critical application, this isn't what you're looking for.
This is free software, licensed under the GNU General Public License.