TripletMail: Replicated E-Mail Storage

We describe TripletMail, a system for outsourcing e-mail backups. The typical corporate mail server that handles receiving, sending and storing e-mails is replaced by two components: A mail server for SMTP/IMAP and a storage system which maintains several encrypted copies of each e-mail in racks of inexpensive servers. In this thesis, we focus on two problems of the storage system: In inexpensive racks, servers can break down often. Therefore, the storage system needs to deal with server failures gracefully and rereplicate copies of e-mails that were lost. Also, storage load should be distributed evenly across all servers. For this, we introduce a scheme that uses consistent hashing to create a key for each e-mail message. A tree then maps parts of the keyspace to triplets of servers on which replicas should be stored. We then describe an approach for re-replication and evaluate this scheme against simpler ones. A Java implementation is included.