Post office staff have been unable to recover any mail from 114 PO boxes which melted when fire tore through the Opononi Four Square.
Sunday night's blaze destroyed the shop but the adjoining hotel was saved by a double firewall, firefighters and a patron armed with a garden hose.
NZ Post spokesman Michael Tull said none of the mail in the PO boxes had survived the fire.
However, there was some good news, because all the mail in the adjacent street posting box was intact. It had been taken to the Whangarei Mail Centre for sorting and delivery.
PO box holders can now collect their mail from the Omapere Foodmart until further notice. They should ask at the counter and bring ID.
Mr Tull said not a lot could be done about mail destroyed in this fire, although box-holders expecting a particular piece of correspondence could contact the sender to see if it could be re-sent.
PO box-holders with specific issues arising from the fire could call the New Zealand Post service centre on 0800 501 501.
The cause of the fire, which started just as owner Paresh Patel was locking up on Sunday night, has been traced to rain leaking into the roof and causing an arc in electrical wiring. Mr Patel had owned the business for less than a year.