“If you made a payment by mail and received an unpaid tax notice from the IRS, you shouldn’t panic yet. Check your records to see how much you paid and compare it to the notice you received. Assuming these numbers match, you may have less to worry about—and if you do owe money, there are steps you can take to resolve it,” writes Kate Dore.
“If you sent the payment by certified mail, double-check to see when the IRS received it. According to CNBC, you won’t owe penalties and fees as long as the agency received your payment before the deadline, July 15.”