For a time after the Anschluss in 1938, letters from Austria to Germany were required to add German stamps, resulting in a mixed franking.

Postal history is the study of postal systems of the past. It includes the study of rates charged, routes followed, and special handling of letters. Areas of special interest include disrupted or transitional periods, such as wars and military occupations, and mail to remote areas. The term has also come to refer to collections of covers and other material illustrating episodes in postal history.

Postal history grew out of philately. As that discipline developed, philatelic students discovered that understanding and authentication of postage stamps depending on knowing why postal administrations issued particular stamps, where they were used, and how. For instance, a stamp apparently used before any other stamp of its type could be proved a forgery if it was postmarked at a location known not have received any stamps until three weeks later.

Postal history has since become a specialty in its own right. There is much that is still not known about the workings of postal systems, and millions of old covers have survived, constituting a rich field of "artifacts" for analysis.

See also: timeline of postal history