The correspondence supports an Oslo court verdict last month that presumed Breivik sane when it found him guilty of the attacks, the book's author Kjetil Stormark said.
Stormark, a journalist who has already published a book on Breivik's July 22nd 2011 attacks that left 77 people dead and shook the Scandinavian nation, has gone through more than 7,000 emails from four accounts used by the 33-year-old right-wing extremist before the massacre.
Most of the emails were business-like, with just a tiny handful sent to loved ones.
"The messages don't give a complete image (of Breivik), but show how patient and empathetic he seems in certain situations," Stormark told
Those traits suggest Breivik is sane and the Oslo court "made the right decision" when it found him of sound mind and sentenced him to prison rather than closed psychiatric care, he said.
On August 24th, the Oslo court handed Breivik Norway's maximum prison term of 21 years, which can be extended if he is still considered a threat to society, for his Oslo bomb attack and shooting rampage on an island.
The book, entitled "The Private Emails of a Mass Killer", is based on correspondence obtained by hackers who accessed Breivik's accounts after the attacks and then gave them to Stormark so he would give them to police, which he did before writing his book.
The emails portray a cold, methodical and rather eloquent Breivik who shows little emotion, in line with the image he presented of himself during his
10-week trial that concluded in June.
There are only a handful of messages sent to loved ones, mostly to his half-sister living in the United States.
"Thanks very much for these great pictures, I'm going to show them to Mum!:D," he writes to his "sis" in March 2010, after the birth of a baby.
"I hope you're feeling a bit better," he wrote, signing off as "Annis" in what could be a phonetic transcription of how a young child would pronounce
his first name.
At the beginning of January 2011, he expressed his condolences to the buyer of one of his weapons after learning of a death in the family.
"I hope that Christmas was OK for you and your family despite this," he wrote.
After the attacks, the first two court-appointed psychiatrists who examined Breivik found him to be suffering from a psychosis, notably citing his lack of emotion.
But a second opinion ordered by the court came to the conclusion that he was criminally sane, a finding later supported by the Oslo court.
The book also publishes a number of exchanges regarding transactions that enabled Breivik to raise money and acquire the equipment necessary for his attacks.
In addition to a never-used rifle that he puts up for sale because he deems it inadequate, Breivik also sells a table service, a set of tyres, a car and
an expensive watch.
At the same time, he buys gear online, including a flashing police light on Ebay in April 2011, three months before the attacks, and pieces of the fake uniform he wore to pass himself off as a police officer on the day of the massacre.
According to Stormark, Breivik could possibly have been detected before the attacks if Norway's intelligence service PST had a computer system capable of correlating suspicious online purchases.
The book also contains messages of support and condemnation sent to Breivik immediately after his attacks.
Breivik's lawyers had protested against the publication of the book, saying it was a violation of his right to privacy.