Dead letter mail or undeliverable mail is mail that cannot be delivered to the addressee or returned to the sender. This is usually due to lack of compliance with postal regulations, an incomplete address and return address, or the inability to forward the mail when both correspondents move before the letter can be delivered. Largely based on the British model that emerged in the late eighteenth century, many countries developed similar systems for processing undeliverable mail.
The term 'dead mail' is perhaps a misnomer, and several jurisdictions have opted for the use of the term 'undeliverable mail' as more clearly representing the status of the item whose transmission has been impeded. As it is performed by internal departments within postal administrations, little information about the dead letter office function has ever been made public. A few journal articles and at least one recently published book (Canadian) dealing with this topic have appeared.
Classification as a dead letter is one of the few instances where postal personnel are allowed to violate secrecy of correspondence, ostensibly to search for clues as to the letter's origin or destination. Countries must also set up regulations for the disposal of dead letters, particularly when they contain items of value. Some very valuable items have turned up in undeliverable mail, including a stolen painting by Marc Chagall which turned up in a United States Postal Service sorting center in Topeka, Kansas in January, 2002.
Many countries, including Canada and the United States, have issued special labels for envelopes that have travelled through the dead letter office. Genuinely used examples are highly prized by collectors, although mint labels, because they have no postage value, are often fairly common.
People interested in postal services throughout the world sometimes deliberately send mail to fictional addresses throughout the world to see if a particular nation's postal authority would return the mail to the sender. Collectors of postal markings also use this method in order to receive uncommon postal markings seldom seen in everyday mail.
A dead letter office (DLO) is a facility within a postal system where undeliverable mail is processed. Mail is considered to be undeliverable when the address is invalid so it cannot be delivered to the addressee, and there is no return address so it cannot be returned to the sender.
At a DLO, mail is usually opened to try to find an address to forward to. If an address is found, the envelope is usually sealed using tape or postal seals, or enclosed in plastic bags and delivered. If the letter or parcel is still undeliverable, valuable items are then auctioned off while the correspondence is usually destroyed. Despite this practice, in the past some undeliverable envelopes were acquired by philatelists.
Dead letter offices go by different names in different countries. Other names include returned letter office or undeliverable mail office.
Canada Post sends mail which is not deliverable to the Undeliverable Mail Office (NUMO) at Mississauga, Ontario, or North Sydney, Nova Scotia. Domestic mail which is still undeliverable after passing through NUMO is then destroyed, while incoming international undeliverable mail is returned to the country of origin.
In Malta, undeliverable mail was sorted in the General Post Office in Valletta. The facility was initially known as the Returned Letter Branch, but later on it was also referred to as the Returned Letter Office or Dead Letter Office. Various postal markings were used at the facility from 1889 onward.
A Dead Letter Office was first established in 1784 for dead and missent letters that had reached London. The bye-letter offices dealt with bye-letters and those that did not go to London. No postage was charged for returns, which were made after six months, where an addressee was found. From 1790, a charge was made for returned letters but the time was reduced to two months by John Palmer. Upon hearing of the return charge William Pitt rescinded the charge.
The U.S. Post Office, as it was known then, started a dead letter office in 1825 to deal with undeliverable mail. By 1893, it handled about 20,000 items every day. In 2006, approximately 90 million undeliverable-as-addressed (UAA) items ended up in the dead-letter office of the U.S. Postal Service; when the rightful owners cannot be identified, the correspondence is destroyed to protect customer privacy, and enclosed items of value are removed. Items of value that cannot be returned are sold at auction, except for pornography and firearms. The auctions also occasionally include items seized by postal inspectors and property being retired from postal service.
These facilities are now known as mail recovery centers (MRC). Other former names include the dead letter branch and the dead parcel branch. The USPS mail recovery center is located in Atlanta, Georgia. Since April 2013, the postal auctions have been held online and include not only material lost in the U.S. but also material from other national postal authorities who consign them to the USPS for auction.