When the Internal Revenue Service believes that a tax return was filed under a stolen identity, it suspends processing of the paperwork and mails an identity verification letter to the taxpayer, according to the IRS. The letter, identified in the upper right corner, is a 5071C.
The IRS mails the 5071C to the address on the tax return; it does not send email. The taxpayer has two methods to verify his identity: by phone or online at IDVerify.irs.gov, using information from the current and previous year's tax returns and supporting documents. Once verified, the taxpayer tells the IRS whether he filed the questioned return. If he did, processing resumes and the taxpayer can expect his refund in about six weeks, notes the IRS.