From the Mainichi Online:
…on June 11, a total of 5.95 million yen was anonymously posted to five public offices — 1 million yen each to the Ministry of Finance, the Meteorological Agency, the Social Insurance Agency and the Board of Audit of Japan, and 950,000 yen to the Ministry of Health, Labor and Welfare. One million yen was also posted to the Gunma Prefectural Library. In each of the cases, the parcels of money bore a June 10 postmark from the Takasaki Post Office in Gunma Prefecture.
There is only one glaring omission from this news story, an interview with the clever clerk that opened the envelope for the Ministry of Health, Labor and Welfare.