Electronic mail is a method of exchanging messages ("mail") between people using electronic devices. Invented by Ray Tomlinson, email first entered limited use in the 1960s and by the mid-1970s had taken the form now recognized as email. Email operates across computer networks, which today is primarily the Internet. Some early email systems required the author and the recipient to both be online at the same time, in common with instant messaging. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver, and store messages. Neither the users nor their computers are required to be online simultaneously; they need to connect only briefly, typically to a mail server or a webmail interface for as long as it takes to send or receive messages or to download it.
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 3501.
Within the Internet email system, a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX host are also used in some contexts.
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.
The Simple Mail Transfer Protocol (SMTP) is a communication protocol for electronic mail transmission. As an Internet standard, SMTP was first defined in 1982 by RFC 821, and updated in 2008 by RFC 5321 to Extended SMTP additions, which is the protocol variety in widespread use today. Mail servers and other message transfer agents use SMTP to send and receive mail messages. Proprietary systems such as Microsoft Exchange and IBM Notes and webmail systems such as Outlook.com, Gmail and Yahoo! Mail may use non-standard protocols internally, but all use SMTP when sending to or receiving email from outside their own systems. SMTP servers commonly use the Transmission Control Protocol on port number 25.
An email client, email reader or more formally mail user agent (MUA) is a computer program used to access and manage a user's email.
Extended SMTP (ESMTP), sometimes referred to as Enhanced SMTP, is a definition of protocol extensions to the Simple Mail Transfer Protocol (SMTP) standard. ESMTP was defined in November 1995 in IETF publication RFC 1869 which established a general structure for all existing and future extensions.
A message submission agent (MSA) or mail submission agent is a computer program or software agent that receives electronic mail messages from a mail user agent (MUA) and cooperates with a mail transfer agent (MTA) for delivery of the mail. It uses ESMTP, a variant of the Simple Mail Transfer Protocol (SMTP), as specified in RFC 6409.
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 new email is actively transferred (pushed) as it arrives by the mail delivery agent (MDA) to the mail user agent (MUA), also called the email client. Email clients include smartphones and, less strictly, IMAP personal computer mail applications.
Opportunistic encryption (OE) refers to any system that, when connecting to another system, attempts to encrypt the communications channel, otherwise falling back to unencrypted communications. This method requires no pre-arrangement between the two systems.
Push-IMAP, which is otherwise known as P-IMAP or Push extensions for Internet Message Access Protocol, is an email protocol designed as a faster way to synchronise a mobile device like a PDA or smartphone to an email server.
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 primarily intended as a countermeasure to passive monitoring.
Ned Freed has contributed as an IETF participant and RFC writer to a significant number of internet protocol standards.
An email box is the destination to which electronic mail messages are delivered. It is the equivalent of a letter box in the postal system.
An email agent is a program that is part of the email infrastructure, from composition by sender, to transfer across the network, to viewing by recipient. The best-known are mail user agents and mail 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.
SMTPS is a method for securing the SMTP using transport layer security. It is intended to provide authentication of the communication partners, as well as data integrity and confidentiality.
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 an Internet protocol for handling the submission and access/synchronization of e-mails, and which was developed to be a possible successor to IMAP.