An Analysis of Database-Driven Mail Servers

This paper compares the performance of three different IMAP servers, each of which uses a different storage mechanism: Cyrus uses a database built on BerkeleyDB, Courier-IMAP uses maildirs, and UW-IMAP uses mbox files. We also use a mySQL database to simulate a relationaldatabase-driven IMAP server. We find that Cyrus and mySQL outperform UW and Courier in most tests, often dramatically beating Courier. Cyrus is particularly efficient at scan operations such as retrieving headers, and it also does particularly well on searches on header fields. UW and Cyrus perform similarly on full-text searches, although Cyrus seems to scale slightly better as the size of the mailbox grows. mySQL excels at full-text searches and header retrieval, but it performs poorly when deleting messages. In general, we believe that a database system offers better email storage facilities than traditional file systems.