Dodgy extract from the current version of the AusPost Word document on the subject, 'DRC_Instructions1.doc':

Service_Type The type of delivery service required. Typically entered by the Consumer from a selection list. Options are :

DOMESTIC
“Standard” = Regular Parcels
“Express” = Express Parcels

INTERNATIONAL
“Air” = Air Mail
“Sea” = Sea Mail
“ECI_D” = Express Courier International Document
“ECI_M” = Express Courier International Merchandise
“EPI” = Express Post International

DOMESTIC
'STANDARD'
'EXPRESS'

INTERNATIONAL
'AIR'
'SEA'
‘ECI_D’
‘ECI_M’
‘EPI’

Cheers
GAM