8 Types of IRS Certified Letters | Certified Mailing | Certified Mail | What is Certified Mail Opening the mail is rarely exciting, but receiving the dreaded IRS-certified mail can send even the calmest person into a frenzy. You may ask yourself why the IRS sent you a certified letter. People typically start mentally combing through their recent filing to determine what might be wrong. Others may head straight to the web to see if they might receive an IRS audit letter due to the certified letter received. You might receive an IRS Certified Letter for several reasons, including an audit letter or an order to identify yourself before the IRS releases a tax refund.