Stamps

Important Events in U.S. Postal History - 1864:
The Act of May 17, 1864 authorized Post Offices to Issue Money Orders in amounts of up to $30. This service was implemented over time, only 141 Post Offices had provided the Money Order Business, "MOB", by November of that year, according to Evans.

The first permanent mobile railway post office, or "RPO", was established with the Chicago and Northwestern Railroad.

The mail was first categorized in three separate classes: "letter postage", "newspapers and magazines" and "miscellaneous mail" which covered just about everything else. These were the predecessors of what we call today, First Class Mail, Second Class Mail, etc.

Commemoratives: The first Commemorative stamps were not issued until 1893
Special Delivery: The first Special Delivery stamps were not issued until 1885
Postage Dues: The first Postage Due Stamps were not issued until 1879