4. Michigan / New Mexico
Michigan/New Mexico has a postal abbreviation whose letters are not in alphabetical order.
The United States Postal Service has provided a two-letter summary for each of the 50 states. Modern Codes consisting of two abbreviated regional and territorial letters began in October 1963, with the release of Publication 59: Abbreviations and ZIP Code, three months after the Post Office Introduced the ZIP codes. Michigan Post Summit (MI) does not match the alphabet. The remaining states of Mississippi (MS), Minnesota (MN), and Missouri (MO) all have two letters of the alphabet.