Nancy Drew: The E-Mail Mystery is an awful book. The author knows almost nothing about computers, so almost all of the information in the book is either wrong or badly outdated. For example, the author believes that emails are sent to phone numbers. I have no idea where the author got that idea.
The main mystery is "Nancy must figure out who sent an email". It takes Nancy over a hundred pages to reach the obvious solution: check the "sent from" section of the email. No, really. She checks the "sent to" section in Chapter 2, but no one thinks to check the "sent from" section until Chapter 15.
After writing my book review, I found out two things about Nancy Drew and technology.
#1, Nancy has a personal computer in the 1987 book Buried Secrets. In The E-Mail Mystery, there is no computer at the Drew house, and Nancy has never used one before.
#2. In the 2013 book Strangers on a Train, Nancy is introduced to Internet search engines for the first time on page 149. Her complete ignorance of computers apparently changed very little in the past 15 years.