The first £600 energy vouchers will start arriving through household letterboxes from January 16.
Delivery of all of the vouchers is expected to take around four weeks and they can only be redeemed at Post Offices.
The vouchers will be sent to those who pay their electricity by credit upon receipt of a bill or via a pre-payment meter - around 500,000 households in Northern Ireland.
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Customers who pay by direct debit are due to receive the £600 support payment automatically into their bank accounts.
Mark Gibson, external affairs manager with Post Office NI, encouraged people to redeem the vouchers as soon as they receive them.
He said: "People will start receiving letters from their energy supplier and along with that letter will be a voucher, and in that letter will detail how they go about redeeming that voucher, and it can only be redeemed at a Post Office.
"Those on direct debit will receive their cash directly into a bank account. They will not receive a letter."
Mr Gibson told BBC's Good Morning Ulster there would be a "phased approach" to delivering the vouchers to households "so that we can manage the cash flow".
They aim to reach the "most vulnerable customers first" in the roll-out.
He added: "We anticipate it will take us four weeks to get all the letters out to customers and that will take us probably to around the middle of February but the vouchers will be redeemable up until the end of March.
"But we would encourage customers to redeem those vouchers as soon as possible obviously to manage the cash flow."
To redeem the voucher, customers will need to bring to the Post Office the letter itself, the voucher, proof of address and photographic ID.
Mr Gibson added: "The one stipulation is that these documents need to have the same name as the voucher on that, so it needs to be able to identify who you are.
"Even if you know the postmaster, which many of our customers do, you still need to bring this information along because that information is required before the voucher can be redeemed."
Customers will be able to redeem the voucher for cash or immediately deposit the money into their bank account while at the Post Office.
Mr Gibson said: "If they bring their bank card they could deposit all or some of that cash into their bank account, and that means they're not worried about walking about with that cash in their pocket. They're not worried about potentially losing it."
He added: "If you do happen to lose the letter or the voucher, it isn't the end of the world. You can contact the energy supplier and we can get another one reissued."
The £600 includes a £400 payment as part of a UK-wide government support scheme and an additional £200 in recognition of Northern Ireland's greater dependence on home heating oil.
Consumers in the rest of the UK have already begun to receive their £400 energy support payment amid the cost-of-living crisis.
There had been uncertainty over the payments to Northern Ireland households due to the region's separate energy market and the collapse of Stormont power-sharing.
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