An email box is the equivalent of a letter box

Letter box

A letter box, letterbox, letter plate, letter hole, mail slot, or mailbox is a receptacle for receiving incoming mail at a private residence or business...

 for electronic mail

Email

Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...

. It is the destination where electronic mail messages are delivered.

Definitions

A mailbox is identified by an email address. However, not all email addresses correspond to a storage facility. The term pseudo-mailbox is sometimes used to refer to an address that does not correspond to a definitive mail store. Email forwarding

Email forwarding

Email forwarding generically refers to the operation of re-sending an email message delivered to one email address on to a possibly different email address...

 may be applied to reach end recipients from such addresses. Electronic mailing list

Electronic mailing list

An electronic mailing list is a special usage of email that allows for widespread distribution of information to many Internet users. It is similar to a traditional mailing list — a list of names and addresses — as might be kept by an organization for sending publications to...

s and email aliases are typical examples.

RFC 5321, defines an email address as a character string that identifies a user to whom mail will be sent or a location into which mail will be deposited. The term mailbox refers to that depository. In that sense, the terms mailbox and address can be used interchangeably.

RFC 5322 defines a mailbox as follows: A mailbox receives mail. It is a 'conceptual entity' that does not necessarily pertain to file storage. It further exemplifies that some sites may choose to print mail on a printer and deliver the output to the addressee's desk, much like a traditional fax

Fax

Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...

 transmission.

Access

An email client retrieves messages from one or more mailboxes. The database (file, directory, storage system) in which the client stores the messages is called the local mailbox.

Popular protocols to retrieve messages are:

• Post Office Protocol
  Post Office Protocol
  In computing, the Post Office Protocol is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection. POP and IMAP are the two most prevalent Internet standard protocols for e-mail retrieval. Virtually all modern...
  
  : a client–server method that is most suitable for reading messages from a single client computer because message are removed from the server mailbox after first retrieval.
• Internet Message Access Protocol
  Internet Message Access Protocol
  Internet message access protocol is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol...
  
  : designed to retrieve messages from multiple clients by allowing remote management of the server mailbox by keeping master copies of messages on the server but can save a copy in the local mailbox.

Web-based clients exist that retrieve messages from the server on behalf of the website user and display them to the user in a suitable format in a web browser

Web browser

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...

.

Storage format

Any kind of database can be used to store email messages. However, some standardization has resulted in several well-known file formats to allow access to a given mailbox by different computer program

Computer program

A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

s. There are two kinds of widely used formats:

• mbox
  Mbox
  mbox is a generic term for a family of related file formats used for holding collections of electronic mail messages. All messages in an mbox mailbox are concatenated and stored as plain text in a single file...
  
   is the original technique of storing all messages in a single file,
• Maildir
  Maildir
  The Maildir e-mail format is a common way of storing e-mail messages, where each message is kept in a separate file with a unique name, and each folder is a directory...
  
   is a newer specification that provides for storing all messages in a directory tree, with one file for each message.

Mailbox names

Mailbox names are the first part of an email address, i.e. the local-part before the @ symbol. The format of email addresses is formally defined in RFC 5322 and RFC 5321. It is often the username of the recipient on the mail server or in the destination domain.

The local-part of an email address may be up to 64 characters long and is case-sensitive.

Valid characters

The local-part of the email address may use any of these ASCII characters:

• Uppercase and lowercase English letters (a–z, A–Z)
• Digits 0 to 9
• Characters ! # $ % & ' * + - / = ? ^ _ ` { | } ~
• Character . (dot, period, full stop) provided that it is not the first or last character, and provided also that it does not appear two or more times consecutively (e.g. John..Doe@example.com).

Reserved names

The following names are sometimes reserved and use internally by various mail handling applications: cur, default, Discard, DRAFTS, INBOX, IMAP, Junk, Junkmail, mbox, mail.txt, new, SENT, SPAM, Spam, tmp, TRASH.