The Shanghai Post Office controlled all post within the Settlement, but post coming in or going out of the treaty port was required to go through the Chinese Imperial Post Office. In 1922 the various foreign postal services, the Shanghai Post Office and the Chinese Post Office were all brought together into a single Chinese Post Office, thus extending the 1914 membership of the Chinese Post Office to the Universal Postal Union to Shanghai Post Office. Some other foreign countries refused to fall under this new postal service's remit, however: for many years, Japan was notable as sending almost all its mail to Shanghai in diplomatic bags, which could not be opened by postal staff.