The big limitation here is that this book concentrates on a couple of open-source packages, so lots of time is spent detailing their intricacies. I would think that a more general book on IMAP4 protocol would be helpful.
But there are good examples of CGI scripts that monitor and manage mail servers, for instance, that can be adapted by the creative sysadmin to many other purposes. I also wish that there was a CD-ROM disc, or website with the source code. Typing in code from a book is a drag. The good thing is that you can modify it and make it your own as you type it in.