List of U.S. state abbreviations - Wikipedia
The purpose, rather than to standardize state abbreviations per se, was to make room in a line of no more than 23 characters for the city, the state, and the ZIP code. Since 1963, only one state abbreviation has changed. Originally Nebraska was "NB"; but, in November 1969, ... Michigan (MI), Minnesota (MN), Missouri (MO), or Montana (MT).
DA: 1 PA: 32 MOZ Rank: 47