Proof of payment is often in the form of adhesive postage stamps, but postage meters are also used for bulk mailing.
Modern private postal systems are typically distinguished from national postal agencies by the names "courier" or "delivery service".
Postal authorities often have functions other than transporting letters.
In some countries, a postal, telegraph and telephone (PTT) service oversees the postal system, in addition to telephone and telegraph systems.
The Universal Postal Union (UPU), established in 1874, includes 192 member countries and sets the rules for international mail exchanges.
In the 19th century the British usually referred to mail as being letters that were being sent abroad (i.e.
on a ship), and post as letters that were for localized delivery; in the UK the Royal Mail delivers the post, while in the USA the US Postal Service delivers the mail.
A postal service can be private or public, though many governments place restrictions on private systems.
Since the mid-19th century national postal systems have generally been established as government monopolies with a fee on the article prepaid.The term email (short for "electronic mail") first appeared in the 1970s.