Until now, the only recognised identity service provider was myGovID which is administered by the Australian Taxation Office.
The TDIF, which is run by the Digital Transformation Agency, sets rules for those who are part of the digital identity system.
Government Services Minister Stuart Robert congratulated Australia Post on the accreditation and said the digital identity federation is designed to have multiple identity providers to give those using the system choice.
"The Morrison Government continues to build trust, privacy and security into the digital identity system. It is designed to ensure that the identity system is reliable, trustworthy and meets user needs.
"This makes sure every government agency and organisation that becomes part of the identity system is held to the same high standards. In the future, we look forward to having many government agencies, banks, or other organisations undergo accreditation to become part of the identity system.
"Providing Australians with choice and control of who they share identity information with was one of the recommendations of the Financial Services Inquiry that we have delivered on."