(NEXSTAR) – Millions of Americans will be receiving their $600 stimulus check in the mail this month, and the Internal Revenue Service urged people Thursday to keep a careful eye on their mailboxes for the plain, white envelope holding their COVID relief payment.

For those who don’t receive a direct deposit, they should watch their mail for either a paper check or a prepaid debit card, the IRS says.

People who received the first stimulus payment as part of the CARES Act in the form of a check may not get their second payment in the same form, and vice versa, the IRS said.

“To speed delivery of the payments to reach as many people as soon as possible the Treasury’s Bureau of Fiscal Service is sending payments out by prepaid debit card,” according to the IRS.

Those physical payments, however, will arrive in plain white envelopes with a U.S. Department of the Treasury seal, so “be sure not to throw it away,” California Senator Dianne Feinstein tweeted last week.

The rollout of the long-awaited second round of stimulus checks has been plagued by delays and routing errors so far and the government is now working to get the payments into the right hands.

“These EIP Cards follow the millions of payments already made by direct deposit and the ongoing mailing of paper checks that are delivering the second round of Economic Impact Payments as rapidly as possible,” the IRS said.

The IRS will be sending out payments until Jan. 15. For more information on the debit card rollout or to track a payment, see the IRS website.