Postmark
A postmark is a postal marking made on a letter or package indicating the approximate date and time that the item was delivered into the care of the postal service. Modern postmarks are often applied simultaneously with the cancellation or "killer" that marks the postage stamp(s) as having been used, and the two terms are often used interchangeably, if incorrectly. Postmarks may be applied by hand or by machines, using methods such as rollers or inkjets.
History
The first postmark (called the "Bishop Mark") was introduced by English Postmaster General Henry Bishop in 1661 and showed only the day and month of mailing in order to prevent the delay of the mail by carriers. In the 19th century and early 1900s it was common for letters to receive multiple postmarks indicating the time, date, and location of each post office delivering or transporting the letter. (While postmarks are applied almost universally by or under the authority of the official postal department, service, or authority, it is at least theoretically possible that under certain conditions specified by the private express statutes in the United States, a privately-carried letter may be cancelled with a private postmark.)
Much of the published work on postmarks covers postmarks from before 1900. (This is perhaps because in the United States so-called fancy cancels were prevalent in this period, with the cancelling device often hand-cut from cork by the postmaster in elaborate shapes such as flags, stars or shapes that were seasonally-appropriate such as turkeys for Thanksgiving). Much work in studying postmarks is needed for 1900 and later.
In Great Britain the first postmark employed for the cancellation of the then new postage stamps was the maltese cross, so named because of its shape and appearance. This was used in conjunction with a date stamp which was applied, usually to the rear of the letter, which denoted the date of posting.
Fewer postmarks are used now than previously, with the advent of meter labels, which indicate the precise date and time of acceptance at the post office, some types of computer vended postage, and computerized postage people can print off their own PCs (called in the United States first day of issue of a particular stamp and pictorial cancellations commemorating local events, anniversaries, and the like and slogan postmarks which advertise and event or pass information to the public.)
Miscellaneous
A datestamp is a type of postmark.
The Postmark Award is given to outstanding employees of Canada Post.
Similar marks
A postmark should not be confused with the killer which are lines, bars, etc. used to cancel a postage stamp. Neither should a postmark be confused with pre-cancels (stamps that have been cancelled before the envelope or package to which they are affixed is submitted or deposited for acceptance into the mailstream, they most commonly have taken the form of a pre-printed city name on the stamp), which generally do not indicate a date.
Flight cachets, more or less elaborate rubber-stamps on an envelope indicating on which flight (typically a first flight) a cover has traveled via air mail, are in addition to the postmark and are not postmarks either.
Source: "Collecting those strange Tongan stamps -- on cover," in Scott Stamp Monthly (August 2002)
