The larger tourist hotels and business towers have convenient post offices from where you can mail letters and small packages. China Post (中国邮政; Zhōngguó Yóuzhèng) offices and post boxes are green.
Useful branches of China Post:
China Post Xīntiāndì Opposite the Site of the 1st National Congress of the CCP.
Letters and parcels take about a week to reach most overseas destinations; Express Mail Service (EMS) cuts this down to three or four days. Courier companies can take as little as two days. Ubiquitous same-day courier companies (快递; kuàidì) can express items within Shànghǎi from around ¥6 within the same district.