The Case for Spam-Aware High Performance Mail Server Architecture

The email volume per mailbox has largely remained low and unchanged in the past several decades, and hence mail server performance has largely remained a secondary issue. The steep rise in the amount of unsolicited emails, i.e. spam, in the past decade, however, has permanently disrupted this tranquility of largely steady email volume and turned mail server performance into an increasingly important issue. In this paper, we point out that modern mail servers were not originally designed with email spam in mind, and as such, as the "common case'' workload for mail servers has shifted from legitimate emails to spam emails, we argue it is time to revisit mail server architecture design in following the system design principle of optimizing the common case. In particular, we show how to optimize the performance of three major components of modern mail servers, the concurrency architecture, the disk I/O, and DNSBL lookups, by exploiting the new "common case" workload. An evaluation of our prototype implementation of the enhanced postfix architecture shows that the optimizations significantly reduce the CPU, disk, and network resource consumptions, and improves the throughput of the mail server by 18\% under a university departmental mail server workload and by 40\% under a spam sinkhole workload.