Although stamp covers and postal history are closely related collecting categories, collectors tend to treat the two pursuits separately. Cover collectors seek out envelopes with stamps affixed to them, usually cancelled and often featuring interesting markings or graphics. These collectors are after first day covers, as well as covers bearing historic dates, unique graphic themes, and fancy cancellations. Of course, they are also interested in a unique and collectible stamp, like the three-cent design appearing on the country's first pre-stamped envelopes in 1853, which were made by the George F. Nesbitt and Co. of New York City.
Postal history collectors are interested in all that, too, but they tend not to be as fixated on stamps. For postal history collectors, being able to chase down the evidence of a letter’s journey from Point A to Point B is often more important than the letter itself, let alone the stamp affixed to it.
One popular cover type is the advertising cover, which is usually collected more for the quality of the illustration, or cachet, on an envelope than for the rarity of its stamp. Advertising covers give the cover collector a lot of information about the sender, and are historical snapshots of a range of goods and services from a particular time.
Disaster covers are letters and envelopes that have been salvaged from shipwrecks, train derailments, airplane crashes, and the like. Mail salvaged from the Hindenburg fire of 1937 is especially collectible (only 200 pieces were salvaged out of the 17,000 that were on board).
More-recent examples of disaster covers are the letters and other pieces of mail that were hand-cancelled on April 3, 2006, the first full day that the U.S. Postal Service resumed normal operations after Hurricane Katrina. Also of interest to collectors is mail that was irradiated during the anthrax scare of 2001. A radiation-burned envelope with the words "Mail Sanitized" on it tells you a lot about that moment in American society.
First day covers, or FDCs, are one of the most popular pursuits of cover collectors. Some collectors focus on events like the 1932 Olympic Games in Los Angeles, others gravitate toward FDCs for that day in July of 1969 when Apollo 11 landed on the moon.
Other first day covers honor individuals. The Series of Famous Americans from 1940 put 35 people like Samuel Clemens, Walt Whitman, Alexander Graham Bell, and Luther Burbank on postage stamps. A Prominent Americans series from 1965 to 1978 featured everyone from Thomas Jefferson to Frank Lloyd Wright to Thomas Paine...
Patriotic covers get us into postal history—some of the most interesting and collectible examples date to the Civil War. In addition to simply looking for evidence of a functioning mail-delivery system from a moment in time (the cancellation stamps, the rates imposed, franking marks, etc.), postal-history buffs try to use that evidence retrace a piece of mail back to its sender. If possible, they will also collect evidence and ephemera associated with the mode of delivery itself, be it Pony Express in the 19th century, Graf Zeppelin in the early part of the 20th, or steamship sailing through the Suez Canal after World War II.
Another collecting category that touches on both covers and postal history is military mail. Here, collectors sometimes look for mail that has been through a particular Army Post Office (APO). Cover collectors can choose from first day covers with cachets of General Eisenhower to the quintet of Civil War Centennial stamps, which were printed one a year from 1961 to 1965.