It's an excellent, well-structured book. Even for an experienced Exim administrator it serves as a great refresher. The specification itself, like all specifications are, and with good reason, is is rather dry. Excellent reference material, and the spec is some of the most excellent
reference material on any software I've ever encountered, on it's own is not enough to feed you ideas.

By reading and re-reading the book, it's a great way to be reminded of features, or condense everything relevant on a particular topic in an easy to digest manner. When changing or adding new configurations, the book is a great first place to look to learn about caveats.

It's one thing to be able to look up features in a spec, but it's completely different to be inspired to use them by being shown how easy they integrate in particular cookbook-like snippets. It's been my experience when reading it that I'll go "Oh yeah, *that* feature, I must enable it", or "Oh yeah, I forgot about that quirk and workaround".

The other great thing about the book is that it's excellent training material. I can hand the book to an exim newcommer and be confident it'll get them up to speed, with the minimum amount of clarifications required.