Splitted Email System
The system uses multiple servers in order to increase fault tolerance but it stores messages encrypted and splitted in order to prevent data leak in case of break-in. Unencrypted messages are never stored on disk, they are decrypted and joined only before presenting them to user. Servers constantly monitor their status and in case of faults they automatically start sending chunks of messages to other servers so that in case of next server breakdown there is no data loss.
Because it's hard to search inside encrypted and splitted messages we've integrated Apache Solr search server into webmail system. Messages are indexed during sending but it doesn't allow to retrieve literal message contents.
We've also added payments system for sending messages and extending message storage time.
Senders can also see if recipient read the message or deleted it. Messages are automatically deleted after seven days, so if it's something important, sender can try to resend the message.
This system is integrated with existing webmail system and users don't need to register separately in this system. Their settings and address book are automatically moved, but messages are stored separately.