A mailbox (also electronic mailbox, email box, email mailbox, e-mailbox) is the destination to which electronic mail messages are delivered. It is the equivalent of a letter box in the postal system. 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 may be applied to reach end recipients from such addresses. Electronic mailing lists 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 transmission. Access Access to a mailbox is controlled by a mailbox provider. Usually, anyone can send messages to a mailbox while only authenticated users can read or delete from their own mailboxes. 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. Read access Popular client–server protocols to retrieve messages are: Post Office Protocol (POP): a method that is most suitable for reading messages from a single client computer. Usually messages are removed from the server mailbox after retrieval. Anyway, the master copy of a message is the one in the local mailbox. Internet Message Access Protocol (IMAP): designed to retrieve messages from multiple clients by allowing remote management of the server mailbox. Master copies stay on the server, but a copy can be saved locally. Webmail over HTTP: messages are served to a user's browser in a server-defined format. Master copies stay on the server, possibly in the original format, which may be downloadable. IMAP and webmail can go along with each other more or less seamlessly. POP, if configured to leave messages on server, can be compatible with them. Internet message format, currently defined by RFC 5322, dates back