IRS Newswire Issue Number IR-2016-123 provides further information on this matter stating:
Generally, the scam involves an email that includes the fake CP2000 as an attachment. The issue has been reported to the Treasury Inspector General for Tax Administration for investigation.
The CP2000 is a notice commonly mailed to taxpayers through the United States Postal Service. It is never sent as part of an email to taxpayers. The indicators are:
IRS impersonation scams take many forms: threatening telephone calls, phishing emails and demanding letters. Learn more at Reporting Phishing and Online Scams.