Police say the powder found two days ago at a mail centre in the Taranaki town of Eltham was not anthrax.
The Ministry of Agriculture and Forestry is still conducting tests to find out what it is.
Results of tests to identify the mystery powders found at six other mail centres overthe last two days are not expected to be available until this evening at the earliest.
The Manukau mail centre in Wiri, south Auckland, re-opened this morning, after being evacuated yesterday following the discovery of an unknown white powder.
The mail handling centre in Eltham remains closed, as do those in Nelson, the Waikato, Wellington, Rotorua, and Linton in Manawatu, however, after workers at those centres also found powders.
