I bet the author doesn't actually know the last time the USPS was subsidized; he just off-handedly argues we shouldn't subsidize it more. (clue: no taxpayer dollars since it was spun off as quasi-governmental)

The USPS is still actively subsidized by the US government, even if it doesn't receive budgeted funds (although they're coming this week to ask for funds and permission to cut service.) The government enforced monopoly on mailbox delivery is effectively a gigantic subsidy, as is their exemption from paying real estate taxes on thousands of buildings they own and vehicles they operate.

An organization doesn't have to receive cash from the government to be heavily government-subsidized - Fannie and Freddie effectively receive billions in subsidies from the government each year because of how much they save on interest via the implied government backing of their obligations. Those kinds of subsidies are far more pernicious because their cost is hidden in a way that budgeted subsidies aren't.