Electronic mail is a method of transmitting and receiving messages using electronic devices. It was conceived in the late–20th century as the digital version of, or counterpart to, mail. Email is a ubiquitous and very widely used communication medium; in current use, an email address is often treated as a basic and necessary part of many processes in business, commerce, government, education, entertainment, and other spheres of daily life in most countries.
In computing, the Internet Message Access Protocol (IMAP) is an Internet standard protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection. IMAP is defined by RFC 9051.
Within the Internet email system, a message transfer agent (MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using the Simple Mail Transfer Protocol. In some contexts the alternative names mail server, mail exchanger, and MX host can be used to describe an MTA.
In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. POP version 3 (POP3) is the version in common use, and along with IMAP the most common protocols for email retrieval.
The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typically use SMTP only for sending messages to a mail server for relaying, and typically submit outgoing email to the mail server on port 587 or 465 per RFC 8314. For retrieving messages, IMAP is standard, but proprietary servers also often implement proprietary protocols, e.g., Exchange ActiveSync.
An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email.
The Maildir e-mail format is a common way of storing email messages in which each message is stored in a separate file with a unique name, and each mail folder is a file system directory. The local file system handles file locking as messages are added, moved and deleted. A major design goal of Maildir is to eliminate the need for program code to handle file locking and unlocking.
A message delivery agent (MDA), or mail delivery agent, is a computer software component that is responsible for the delivery of e-mail messages to a local recipient's mailbox. It is also called a local delivery agent (LDA).
procmail is an email server software component — specifically, a message delivery agent (MDA). It was one of the earliest mail filter programs. It is typically used in Unix-like mail systems, using the mbox and Maildir storage formats.
An email address identifies an email box to which messages are delivered. While early messaging systems used a variety of formats for addressing, today, email addresses follow a set of specific rules originally standardized by the Internet Engineering Task Force (IETF) in the 1980s, and updated by RFC 5322 and 6854. The term email address in this article refers to just the addr-spec in Section 3.4 of RFC 5322. The RFC defines address more broadly as either a mailbox or group. A mailbox value can be either a name-addr, which contains a display-name and addr-spec, or the more common addr-spec alone.
A bounce message or just "bounce" is an automated message from an email system, informing the sender of a previous message that the message has not been delivered. The original message is said to have "bounced".
Apple Open Collaboration Environment (AOCE) is a collection of messaging-related technologies introduced for the Classic Mac OS in the early 1990s. It includes the PowerTalk mail engine, which is the primary client-side interface to the system, the PowerShare mail server for workgroup installations, and a number of additional technologies such as Open Directory, encryption, and digital signature support.
Email filtering is the processing of email to organize it according to specified criteria. The term can apply to the intervention of human intelligence, but most often refers to the automatic processing of messages at an SMTP server, possibly applying anti-spam techniques. Filtering can be applied to incoming emails as well as to outgoing ones.
Push email is an email system that provides an always-on capability, in which when new email arrives at the mail delivery agent (MDA), it is immediately, actively transferred (pushed) by the MDA to the mail user agent (MUA), also called the email client, so that the end-user can see incoming email immediately. This is in contrast with systems that check for new incoming mail every so often, on a schedule. Email clients include smartphones and, less strictly, IMAP personal computer mail applications.
In computer networking, a port or port number is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system, a port is a logical construct that identifies a specific process or a type of network service. A port at the software level is identified for each transport protocol and address combination by the port number assigned to it. The most common transport protocols that use port numbers are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP); those port numbers are 16-bit unsigned numbers.
Email forwarding generically refers to the operation of re-sending a previously delivered email to an email address to one or more different email addresses.
A mailbox is the destination to which electronic mail messages are delivered. It is the equivalent of a letter box in the postal system.
MCI Mail was one of the first commercial email services in the United States and one of the largest telecommunication services in the world. Operated by MCI Communications Corp. from 1983 to 2003, MCI Mail offered its customers a low cost and effective solution for sending and receiving electronic mail.
An e-mail agent is a program that is part of the e-mail infrastructure, from composition by sender, to transfer across the network, to viewing by recipient. The best-known are message user agents and message transfer agents, but finer divisions exist.
A mailbox provider, mail service provider or, somewhat improperly, email service provider is a provider of email hosting. It implements email servers to send, receive, accept, and store email for other organizations or end users, on their behalf.
