There is very little specialist literature available on IMAP servers, and no
current documentation deals with the subject in sufficient depth.
There is a real need for a guide to IMAP. A quick look at relevant mailing
lists shows that they are full of questions and problems, indicating that the
software solutions now in use raise many issues. IMAP may seem to be a
simple affair and to require little in the way of configuration, but there are
plenty of pitfalls when an IMAP server is designed for a large number of
users or when elaborate additional features are added to a basic installation.
We have specialized in Courier and Cyrus during the last few years. Both
offer distinct advantages and disadvantages, so the appropriate choice of
software depends on the project. Peer Heinlein mainly works with Courier
IMAP, and he uses it to implement mail servers for large ISPs that are
designed to accommodate tens or hundreds of thousands of users. Peer
Hartleben uses Cyrus IMAP for mail servers in small and large companies,
which require Cyrus user administration—sometimes via a console—
and server-based filtering of mail using Sieve. Peer Heinlein has therefore
written the introduction and the Courier section of this book, and Peer
Hartleben has written the section on Cyrus.
Neither Courier nor Cyrus have had suitable documentation (until now).
We have to admit: This book was hard work. There were many behaviors
and call parameters that we had to debug and test by trial and error, or
understand by analyzing the source code, because their significance was
not documented anywhere. The project mailing lists often were not helpful,
frequently containing more questions than answers.
The detailed work on this book took far longer than we had originally suspected
it would, and there were repeated delays in publication. But, finally,
we have an exhaustive and up-to-date reference on the subjects of IMAP,
Courier, and Cyrus. Considering the importance of email communication,
we hope that this book will help many administrators and postmasters in