Mail service, postal service, post (the system whereby messages are transmitted via the post office) "the mail handles billions of items every day.
It is a system for transporting letters and other tangible objects: written documents, typically enclosed in envelopes, and also small packages are delivered to destinations around the world. Anything sent through the postal system is called mail or post.
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. Proof of payment is often in the form of adhesive postage stamps, but postage meters are also used for bulk mailing.
Postal authorities often have functions other than transporting letters. In some countries, a Postal Telegraph and Telephone (PTT) service oversees the postal system as well as having authority over telephone and telegraph systems. Some countries' postal systems allow for savings accounts and handle applications for passports.