Modern mail is organized by national and privatized services, which are reciprocally interconnected by international regulations, organizations and international agreements. Paper letters and parcels can be sent to almost any country in the world relatively easily and cheaply. The Internet has made the process of sending letter-like messages nearly instantaneous, and in many cases and situations correspondents use electronic mail where previously they would have used letters (though the volume of paper mail continues to increase.)

Organization

In the United States, private companies such as FedEx and UPS compete with the federal government's United States Postal Service, particularly in package delivery. Different mailboxes are also provided for local and express service. (The USPS has a monopoly on First Class and Standard Mail delivery.)

Some countries have organized their mail services as public limited liability corporations without a legal monopoly.

The worldwide postal system comprising the individual national postal systems of the world's self-governing states is co-ordinated by the Universal Postal Union, which among other things sets international postage rates, defines standards for postage stamps and operates the system of International Reply Coupons.

In most countries a system of codes has been created (they are called ZIP Codes in the United States, postcodes in the United Kingdom and Australia, and postal codes in most other countries), in order to facilitate the automation of operations. This also includes placing additional marks on the address portion of the letter or mailed object, called "bar coding." Bar coding of mail for delivery is usually expressed either by a series of vertical bars, usually called POSTNET coding, or a block of dots as a two-dimensional barcode. The "block of dots" method allows for the encoding of proof of payment of postage, exact routing for delivery, and other features.

The ordinary mail service was improved in the 20th century with the use of planes for a quicker delivery (air mail). The first scheduled airmail service took place between the London suburbs of Hendon and Windsor on 9 September 1911. Some methods of airmail proved ineffective, however, including the United States Postal Service's experiment with rocket mail.

Receipts services were made available in order to grant the sender a confirmation of effective delivery.

Mail going to naval vessels is known as the Fleet Post Office.

Zabrze (Poland) - post office

Postal truck in Brazil

Delivery by bicycle in Germany

Payment

Worldwide the most common method of prepaying postage is by buying an adhesive postage stamp to be applied to the envelope before mailing; a much less common method is to use a postage-prepaid envelope. Franking is a method of creating postage-prepaid envelopes under licence using a special machine. They are used by companies with large mail programs such as banks and direct mail companies.

In 1998, the U.S. Postal Service authorised the first tests of a secure system of sending digital franks via the Internet to be printed out on a PC printer, obviating the necessity to license a dedicated franking machine and allowing companies with smaller mail programs to make use of the option; this was later expanded to test the use of personalised postage. The service provided by the U.S. Postal Service in 2003 allows the franks to be printed out on special adhesive-backed labels. In 2004 the Royal Mail in the United Kingdom introduced its SmartStamp Internet-based system, allowing printing on ordinary adhesive labels or envelopes. Similar systems are being considered by postal administrations around the world.

When the pre-paid envelope or package is accepted into the mail by an agent of the postal service, the agent usually indicates by means of a cancellation that it is no longer valid for pre-payment of postage. The exceptions are when the agent forgets or neglects to cancel the mailpiece, for stamps that are pre-cancelled and thus do not require cancellation and for, in most cases, metered mail. (The "personalised stamps" authorized by the USPS and manufactured by Zazzle and other companies are in fact a form of meter label and thus do not need to be cancelled.)

Rules and etiquette

"The Steamboat" - mobile steaming equipment used by Czech StB for unsticking of envelopes during correspondence surveillance and censorship

Documents cannot be read by anyone other than the receiver; for instance, in the United States it is a violation of federal law for anyone other than the receiver to open mail. However, exceptions do exist, such as postcards, which can be read by the postman for the purpose of identifying the sender and receiver. For mail contained within an envelope, there are legal provisions in some jurisdictions allowing the recording identities. The privacy of correspondence is guaranteed by the Mexican Constitution, and is alluded to in the European Convention of Human Rights and the Universal Declaration of Human Rights. According to the laws in the relevant jurisdiction, correspondence may be openly or covertly opened or the contents determined via some other method, by the police or other authorities in some cases relating to their relevance to an alleged or suspected criminal conspiracy, although black chambers (largely in the past, though there is apparently some continuance of their use today) opened and open letters extralegally. Military mail to and from soldiers on active deployment is more often subject to strict censorship. International mail and packages are subjects to customs control.

Control of private citizens' mail based on its content is a form of censorship and concerns social, political, and legal aspects of civil rights. Even though often illegal, there have been cases over the centuries of governments illegally opening and copying or photographing the contents of private mail. While in most cases this censorship is exceptional, in the military, censorship of mail is routine and almost universally applied, particularly with respect to soldiers near a battlefront.

Modern alternatives such as the telegraph, telephone, telex, facsimile, and e-mail have reduced the attractiveness of paper mail for many applications. Sometimes these modern alternatives are more attractive because, unlike paper mail, there is no concern about unfamiliar people learning your address from the return address on the outside of an envelope. Modern alternatives can be better than paper mail because vandalism can occur with mailboxes (although it can also be argued that paper mail does not allow for computer viruses). Also, dangerous hazards exist for mail carriers such as unfriendly pets or bad weather conditions. Due to hazards or inconveniences postal carriers may refuse, officially or otherwise, to deliver mail to a particular address (for instance, if a clear path to the door or mailbox is not present). Postal mail is, however, still widely in use for business (due to the particular legal standing of signatures in some situations and in many jurisdictions, etiquette, or transmission of things that cannot be done by computer, as a particular texture, or, obviously, items in packages) and for some personal communication. For example, wedding invitations in some Western countries are customarily sent by mail.

Rise of electronic correspondence

Since the advent of e-mail, which is universally faster (barring some extreme technical glitch, computer virus or the like), the postal system has come to be referred to in Internet slang by the retronym "snail mail". Occasionally, the term "white mail" or "the PaperNet" has also been used as a neutral term for postal mail.

In modern times, mainly in the 20th century, mail has found an evolution in vehicles using newer technologies to deliver the documents, especially through the telephone network; these new vehicles include telegram, telex, facsimile (fax), e-mail, and short message service (SMS). There have been methods which have combined mail and some of these newer methods, such as INTELPOST, which combined facsimile transmission with overnight delivery. These vehicles commonly use a mechanical or electro-mechanical standardised writing (typing), that on the one hand makes for more efficient communication, while on the other hand makes impossible characteristics and practices that traditionally were in conventional mail, such as calligraphy.

This epoch is undoubtedly mainly dominated by mechanical writing, with a general use of no more of half a dozen standard typographic fonts from standard keyboards. However, the increased use of typewritten or computer-printed letters for personal communication and the advent of e-mail, has sparked renewed interest in calligraphy, as a letter has become more of a "special event." Long before e-mail and computer-printed letters, however, decorated envelopes, rubber stamps and artistamps formed part of the medium of mail art.

In the 2000s with the advent of eBay and other online auction sites and online stores, postal services in industrialized nations have seen a major shift to item shipping. This has been seen as a boost to the system's usage in the wake of lower paper mail volume due to the accessibility of e-mail.

Online post offices have emerged to give recipients a means of receiving traditional correspondence mail in a scanned electronic format.

Collecting

Postage stamps are also object of a particular form of collecting, and in some cases, when demand greatly exceeds supply, their commercial value on this specific market may become enormously greater than face value, even after use. For some postal services the sale of stamps to collectors who will never use them is a significant source of revenue for example postage stamps from Tokelau, South Georgia & South Sandwich Islands, Tristan da Cunha, Niuafo´ou and many others. Stamp collecting is commonly known as philately, although strictly the latter term refers to the study of stamps.

Another form of collecting regards postcards, a document written on a single robust sheet of paper, usually decorated with photographic pictures or artistic drawings on one of the sides, and short messages on a small part of the other side, that also contained the space for the address. In strict philatelic usage, the postcard is to be distinguished from the postal card, which has a pre-printed postage on the card. The fact that this communication is visible by other than the receiver often causes the messages to be written in jargon.

Letters are often studied as an example of literature, and also in biography in the case of a famous person. A portion of the New Testament of the Bible is composed of the Apostle Paul's epistles to Christian congregations in various parts of the Roman Empire. See below for a list of famous letters.

A style of writing, called epistolary, tells a fictional story in the form of the correspondence between two or more characters.

A make-shift mail method after stranding on a deserted island is a message in a bottle.

Deregulation

Several countries, including Sweden (1 January 1993), New Zealand (1998 and 2003), Germany (2005 and 2007) and Argentina have opened up the postal services market to new entrants. In the case of New Zealand Post Limited, this included (from 2003) its right to be the sole New Zealand postal administration member of the Universal Postal Union, thus the ending of its monopoly on stamps bearing the name New Zealand.