Habe die chinesischen Schriftzeichen auf dem Brief übersetzen lassen, und das kam dabei heraus:

Seite 1 (mit Marken)
- Year of Xin Chou. This is year’s name in old Gregorian-Lunar Calendar. It maybe 1901, 1961, 2021, etc. In this particular case it cannot be later than 1961, since this is only used in ancient China.
- Express delivery
- Month of Qing He. This means April in ancient China. Few people know this name now.
- 15th Day of a (lunar) month

Seite 2 (mit rotem Band)
- Please deliver this letter to Qingdao (Tsingtau), Dasen Trading Company, Mr. Zhang Shanbao
- From Shanghai, by Chen Rongquan
- Private