A World Without Email

First half of the book, pages is a bunch of interesting case studies and a description of the problems with email. The author also quotes from academic papers and research, given his background as a Professor. The basic problem is that we tend to keep checking mail throughout the day, which keeps us distracted from actual deep work.
Interesting quotes:
“Those who retained access to Marshall were provided a clear structure for their interactions, turning briefing the general into an exercise in controlled efficiency. You were instructed to enter his office and sit down without saluting (to save time). At Marshall's signal, you would begin your brief while he listened with “absolute concentration.” If he discovered a flaw or something missing, he would become angry that you hadn't noticed and resolved the issue before wasting his time. When you finished, he'd ask for your recommendation, deliberate briefly, then make a decision. He then delegated taking action on the decision back to you.” – a model for manager-employee communication.
Try reducing your actual working hours from the existing ones to maybe 2 hours lesser, and see how you are able to finish your work in the reduced time. It will make you prioritise better and also prevent you from stretching your work just to fill up the timeclock. It will also reduce context switching, and thus overload.
“If people trust you to handle the work they send your way, then they're generally fine with not hearing back from you right away. On the other hand, if you're flaky, others will demand faster responses, as they'll feel they have to stay on you to ensure things get done.”
“He notes that without this structure, you're left with only one option for increasing productivity: figuring out how to get people to “work faster.” Once you see the whole process, however, a much more powerful option emerges: “We can change the nature of the work performed.” Optimize processes, he urged, not people.”
“An email arrives that informally represents a new responsibility for you to manage; because there's no formal process in place to assign the work or track its progress, you seek instead the easiest way to get the responsibility off your plate—even if just temporarily—so you send a quick reply asking for an ambiguous clarification. Thus unfolds a game of obligation hot potato, as messages bounce around, each temporarily shifting responsibility from one inbox to another, until a deadline or irate boss finally stops the music, leading to a last-minute scramble to churn out a barely acceptable result.”
“As Johnson explained, the manager in question has a schedule that begins every day with three hours of uninterrupted deep work before he receives “even a single input.” This is time set aside for the manager to think intensely about his projects—making informed decisions on how to go forward, where to focus next, what to improve, and what to ignore. Only after this morning block ends does the manager turn his attention to actively managing the projects he runs.”
“Every employee of Optimize is expected to spend at least the first ninety minutes of every day in a deep work block, free from inputs (some people, like the manager profiled above, spend much more). One of the key uses of this morning block is to think about processes and how to improve them.”

The Protocols part of the book is extremely insightful, and has plug-and-play principles which can be applied.
On the whole, this book will have its biggest impact on you if you know Newport's style of writing, and have read his previous books, especially Deep Work.