The first American service of this type was the U.S.-German Seapost, which began operating in 1891 on the S.S. Havel North German Lloyd Line.
The Seapost service still employed fifty-five clerks in early 1941.
The last route of this type (to South America) was terminated October 19, 1941, due to unsafe wartime conditions on the Atlantic Ocean.
The few remaining Seapost clerks transferred to branches of the Railway Mail Service (RMS).
Seapost offices were also operated by the postal authorities of France, Germany, Great Britain, Italy, Japan and New Zealand.