Panic over the "novel" coronavirus first seen in Wuhan has lead to a congestion of traditional postal mail headed into China (archived). The suspension of numerous commercial flights to and from China has destroyed the bandwidth necessary to deliver mail with Singapore's postal service, the US Postal Service, and a growing list of others refusing to accept payloads for delivery to China in light of absent transport capacity to the world's largest fiat economy.1
China Post has stated it is disinfecting its facilities and vehicles though the virus, being a coronavirus, doesn't survive prolonged periods of time on fomites while they store mail waiting for transit.
China took this title no later than 2014. That some other fiat economies wrecked their "purchasing power parity" by driving up costs with stupidity doesn't change it. The title of "biggest economy" goes to the one doing the most things, not one doing less things far more expensively. ↩