The sub-title says it all: Matt Blumberg's book focuses on newsletters - by which he means promotional emails the recipient actively subscribed to. He doesn't spend any time on unsolicited promotional emails that a company sends to its customer base. Nevertheless, the content and optimization strategies he suggests hold true for both kinds of mailings. Only the list strategies he describes mostly apply only to subscription emails.
Blumberg's style is very much to the point. Some paragraphs read as if there were an exclamation mark at the end of each sentence. He tells the reader how email marketing should be done - and he does so in a manner that's easy to understand, using lots of examples and a clear language. While this is probably the right approach for anyone getting started in email marketing, anyone with a bit of experience in this area would have appreciated more background in some chapters. Especially since one feels that Blumberg omits some details on purpose in order to recommend enlisting the services of an agency - which leaves a bad aftertaste, since Blumberg is the founder and CEO of the email marketing agency Return Path.
That being said "Sign Me Up" is still a well-written, well-structured introduction to email marketing that covers the most important aspects of the trade.