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), 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, or MX host are used to describe an MTA.
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.
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).
The Cyrus IMAP server is electronic mail server software developed by Carnegie Mellon University. It differs from other Internet Message Access Protocol (IMAP) server implementations in that it is generally intended to be run on sealed servers, where normal users cannot log in.
Dovecot is an open-source IMAP and POP3 server for Unix-like operating systems, written primarily with security in mind. Timo Sirainen originated Dovecot and first released it in July 2002. Dovecot developers primarily aim to produce a lightweight, fast and easy-to-set-up open-source email server.
The UW IMAP server was the reference server implementation of the Internet Message Access Protocol. It was developed at the University of Washington by Mark Crispin and others.
Sieve is a programming language that can be used for email filtering. It owes its creation to the CMU Cyrus Project, creators of Cyrus IMAP server.
In cryptography, CRAM-MD5 is a challenge–response authentication mechanism (CRAM) based on the HMAC-MD5 algorithm. As one of the mechanisms supported by the Simple Authentication and Security Layer (SASL), it is often used in email software as part of SMTP Authentication and for the authentication of POP and IMAP users, as well as in applications implementing LDAP, XMPP, BEEP, and other protocols.
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.
The Simple Mail Access Protocol (SMAP) is an application layer Internet protocol for accessing email stored on a server. It was introduced as part of the Courier suite, with the goal of creating a simpler and more capable alternative to IMAP.
Opportunistic TLS refers to extensions in plain text communication protocols, which offer a way to upgrade a plain text connection to an encrypted connection instead of using a separate port for encrypted communication. Several protocols use a command named "STARTTLS" for this purpose. It is a form of opportunistic encryption and is primarily intended as a countermeasure to passive monitoring.
A mailbox is the destination to which electronic mail messages are delivered. It is the equivalent of a letter box in the postal system.
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.
SMTP Authentication, often abbreviated SMTP AUTH, is an extension of the Simple Mail Transfer Protocol (SMTP) whereby a client may log in using any authentication mechanism supported by the server. It is mainly used by submission servers, where authentication is mandatory.
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.
The JSON Meta Application Protocol (JMAP) is a set of related open Internet Standard protocols for handling email. JMAP is implemented using JSON APIs over HTTP and has been developed as an alternative to IMAP/SMTP and proprietary email APIs such as Gmail and Outlook. Additional protocols and data models being built on top of the core of JMAP for handling contacts and calendar synchronization are meant to be potential replacements for CardDAV and CalDAV, and other support is currently in the works.
