I purchased and read The Book of Postfix because I'm always interested in learning something new. This certainly is one hell of a book! I'm an Exim guy myself, and I swear by the magic that Exim lets me do with a piece of mail. Ralf Hildebrandt and Patrick Koetter have certainly done a fabulous job with their book, and they have managed to make me consider using Postfix on my next project. They concisely, clearly and very beautifully bring forward how to use Postfix in real-world situations. Clear diagrams illustrate every concept, and the book is packed full of tips & real-world configurations, including exporting users from a Microsoft Exchange server to use in a Postfix gateway. I think the book is worth its price in chapter fifteen alone: Understanding SMTP Authentication carries the only decent documentation about Cyrus SASL(Simple Authentication and Security Layer) I've ever had the pleasure to read. An invaluable resource for any LDAP guy as well! All in all, a most pleasurable experience.