According to a 4/10/13 CNET article, the IRS thinks it doesn’t need a warrant to read taxpayer emails in pursuit of tax collection. The files were released to the American Civil Liberties Union, under a Freedom of Information Act request, which demonstrates that the IRS broadly interprets their authority to “snoop through” U.S. taxpayer “inboxes”.
The IRS has a “legal leg to stand on”: The Electronic Communications Privacy Act allows the IRS to obtain emails older than 180 days without a warrant. An internal 2009 IRS document claimed that “the government may obtain the emails that have been in storage for more than 180 days without a warrant.”
Another 2009 IRS file, the IRS Criminal Tax Division’s “Search Warrant Handbook”, showed “the 4th Amendment does not protect communications held in electronic storage, because ‘internet users’ do not have a reasonable expectation of privacy”.
In December 2010, the 6th Circuit Court of Appeal ruled that just because your email is held in storage does not mean you lose that expectation of privacy, precluding federal and local law information from reviewing contents of U.S. taxpayer emails.
However, the 6th Circuit Court of Appeal was just the ruling of one appeals court, not the Supreme Court, and the IRS’ stated position is “the IRS does not need a warrant for emails older than 180 days”.