Scaling up Cambridge University’s email service

One of the central services provided by the University of Cambridge Computing Service is the email system, Hermes. Since its introduction in 1993 it was based on UW-IMAP and a shared Unix filestore. This architecture has a number of inherent limitations in performance, scalability, resilience, and cost-effectiveness. In order to address these problems, and particularly users’ desire for larger messages and disk quotas, the system is being replaced with a mostly-compatible reimplementation based on multiple CMU Cyrus message stores. This paper explains the effects of the limitations of the old system, including the restrictions imposed on our users, and the implementation of our webmail software, Prayer. We describe how Cyrus has been modified to make the transition to the new system easier, and to address the anticipated reliability and administration problems caused by using more inexpensive hardware. Finally, after covering the changing role of our central email relay in the new architecture, we discuss some possible development projects for the future.