Managing IMAP

Chapter 16. Server Performance Tuning

Although you may very well want your IMAP server to appear as a black box to your users, it should never appear so to you. In this chapter, we’ll focus on a few hints that pertain primarily to IMAP servers.

Platform

On what platform should you run your IMAP servers? This is indeed the sixty-four-thousand-dollar question.

Broadly speaking, IMAP servers have many of the same requirements as other server machines. An IMAP server must be robust enough to handle a large number of connections and processes. It must also be able to stay up “24-by-7” so that users have confidence in the service. It should have enough memory and disk to store and process large amounts of mail without significant variations in performance.

The type of server platform that is able to provide that level of performance depends on your user base. As we mentioned earlier, a desktop machine (e.g., an Intel Pentium II with a 9 GB disk and 64 MB of memory, running Solaris X86, Linux, or FreeBSD) works just fine in some environments—e.g., a small company with 100 to 200 employees or an ISP with 500 to 1,000 customers.

Customers of a large ISP, however, might be far less forgiving of intermittent outages for maintenance than corporate users, who may not even notice an outage at four o’clock in the morning. Unless you use some sort of high-availability scheme like IP load-balancing or server clustering, we recommend that your servers exploit server-quality (or server-class) ...