ElasticInbox is reliable, distributed, scalable email store.
ElasticInbox provides highly available email store without a single point of failure which can run on commodity hardware and scale linearly. ElasticInbox can easily scale to millions of mailboxes, with hundreds of thousands messages in each mailbox.
Please visit http://www.elasticinbox.com/ for more information.
To build and run from source you will need Maven 3 and Git:
% git clone git://github.com/elasticinbox/elasticinbox.git elasticinbox
% cd elasticinbox
% mvn clean install pax:provision -DskipITs
Licensed under the Modified BSD License.