About 1.5 million letters and packages could not be delivered after 38 of 1,200 post offices were submerged.
Thailand Post normally receives and delivers about 5 million parcels per day.
Piyawat Mahapauraya, senior executive vice president, said yesterday that the company continued to operate as usual.
However, in deeply flooded areas, postal carriers cannot make their rounds and many people are not at home. The parcels will be delivered when the flood subsides.
To serve private and state offices on Vibhavadi-Rangsit, Chaeng Wattana and other swamped Bangkok roads, large trucks are being used, Piyawat said. The company is providing transport for its employees to its head office on Chaeng Wattana and paying a daily allowance of Bt100 to those working during the flooding, he added.