The TURN command used for this purpose posed a security risk because it caused the SMTP session to reverse direction and begin sending the stored mail immediately without any verification or authentication that the requesting server was actually who it claimed to be. ETRN starts a new SMTP session rather than reversing direction. Thus if the server making the request is a “spoofed” host, the sending server will still attempt to deliver the mail to the real host instead. There is now a proposed standard that introduces Authenticated TURN (ATRN), which, like TURN, reverses the direction of the SMTP session but requires authentication before doing so. This new standard is On-Demand Mail Relay (ODMR). MCSC servers support both ETRN and ODMR’s ATRN.

Email (Close this window when finished and you will be returned to where you started)
Stands for “Electronic mail”. This term also appears in the forms: “E-mail”, “e-mail”, and “email”; all have the same meaning. Email is the transmission of text messages over communications networks. Most computer networks have some form of email system. Some email systems are confined to a single computer network, but others have gateways to other networks (which enables them to communicate with multiple locations), or to the Internet (which enables them to send email anywhere in the world).

Most email systems include some form of email client (also referred to as a mail client or just client) which contains a text editor and other tools for composing messages, and one or more servers which receive the email from the clients and route it to its appropriate destination. Typically, a message is composed using the client, passed to a server for delivery to the email address (or addresses) specified in the message, and then routed by the server to another server that is responsible for storing messages destined for that address. If the message’s destination is a local address for which the original server is responsible then it may be stored on the original server rather than routed to another. Last, the recipient of the message will connect to their server and retrieve the message by using their email client. This entire process of transferring an email message from your client to its destination server usually only takes a few seconds or minutes.

Besides containing simple text, email messages may also include file attachments. These attachments can be any type of file that you desire: pictures, text files, program files, other email messages, and so on. However, since most email systems only support sending text files, attachments must first be encoded (converted to a text format) before they can be sent, and then decoded when they arrive at their final destination. This process is usually done automatically by the sending and receiving mail clients.

Gateway (Close this window when finished and you will be returned to where you started)
Computer hardware or software that translates data between two applications or networks with protocols that are dissimilar. “Gateway” is also used to describe any means by which access is provided from one system to another. For example, your ISP is a gateway to the Internet.

Our email servers can function as an email gateway for other domains. It acts as an intermediary, or Gateway, by collecting the domain’s email and then holding it until the domain collects it. This is useful both for domains that do not maintain a continuous connection to the Internet and for domains that require a backup server in case theirs goes down.

Host (Close this window when finished and you will be returned to where you started)
Any computer on a network that acts as a server for other computers on the same network. The host machine may be running a web server, email server, or other services, and it is common for it to provide several services at once. Host is also often used in the verb form “to host”. For example, a machine running an email server would be “hosting” the email.

IMAP (Close this window when finished and you will be returned to where you started)
Developed by Stanford University, Internet Message Access Protocol (IMAP) is a protocol used for managing and retrieving email messages. The latest version is IMAP4 and is similar to POP3 but with a number of additional features. IMAP4 is best known as a protocol used for managing email messages on the server rather than on the user’s local machine—messages can be searched for keywords, organized in folders, specifically selected for downloading, and other features, all while they are still on the server. Thus IMAP places less demand on the user’s machine and centralizes email so that it can be accessed from multiple locations.

IP Address (Close this window when finished and you will be returned to where you started)
Occasionally called an IP Number, IP Address stands for Internet Protocol Address and is used to identify a particular TCP/IP network and the hosts or machines on that network. It is a 32-bit numeric address containing four numbers between 0 and 255 separated by dots (e.g. “127.0.0.1”). Every computer on the Internet must have a registered IP address to avoid duplication. Each Internet IP address can be either static or dynamic. Static addresses do not change and always represent the same location or machine on the Internet. Dynamic IP addresses change and are usually assigned by an ISP to computers that are only on the Internet temporarily—such as when a user with a dial-up account accesses the Internet. However, it is still possible for a dial-up account to have a static IP address assigned to it.

ISP (Close this window when finished and you will be returned to where you started)
An Internet Service Provider (ISP) is a company that provides Internet access and services to the end user. Most ISPs provide multiple Internet services to their customers, such as: WWW access, email, access to newsgroups and news servers, and so on. Typically, users will connect to their ISP via dial-up, or some other form of connection, and then the ISP will connect them to a router, which will in turn route them to the Internet backbone.

LAN (Close this window when finished and you will be returned to where you started)
A Local Area Network (LAN) is a computer network limited to a single building or area, usually having all nodes (computers or workstations) connected together with some configuration of wires or cables or some other form of media. Most large companies have a LAN, which greatly simplifies the management and sharing of information amongst employees and offices. Most LANs utilise some form of email or chat system, and share devices such as printers in order to avoid having to have a separate device for each station. When the network’s nodes are connected together via phone lines, radio waves, or satellite links it is called a Wide Area Network (WAN) instead of LAN.

Mailbox (Close this window when finished and you will be returned to where you started)
An area in memory or on a storage device that is assigned to a specific email address and where email messages are stored. In any email system, each user has a private mailbox in which messages are stored when that user’s mail server receives them. It is also common for the term “mailbox” to be used when referring to the leftmost portion of an email address. For example, “Frank” in “Frank@mcsc.co.za” is the mailbox while “mcsc.co.za” is the domain name.

Mailing List (Close this window when finished and you will be returned to where you started)
Also called email groups, a mailing list is a list or group of email addresses identified by a single email address. For example, “listname@example.com”. Typically when a list server receives an email message addressed to one of its mailing lists that message will be automatically distributed to all of the list’s members (i.e. the addresses included in the list). Our servers are equipped with an extensive suite of mailing list features that enable lists to be public or private (anyone can post or join, or only members can post or join), moderated (each message must be approved by someone before it will go to the list), sent in digest format or as individual messages, and used in a variety of other ways.

ODMR (Close this window when finished and you will be returned to where you started)
On-Demand Mail Relay is a new protocol designed to enable mail servers with only an intermittent connection to a service provider, and which do not have a static IP address, to receive mail similarly to those servers that do have one and use the ETRN command. If the system has a static IP address, the ESMTP ETRN command can be used. However, systems with dynamic IP addresses have no widely deployed solution. ODMR solves this problem. Among other things, ODMR introduces the Authenticated TURN command (ATRN) which causes the flow of an SMTP session to be reversed (like the older TURN command) but with the added security of requiring that the requesting server be authenticated. This makes it possible for an SMTP server with a dynamic IP address to connect to its ISP and have one or more host’s email delivered to it via SMTP rather than collect it via POP or IMAP. This helps meet the widespread demand for a low-cost solution for those companies that need to their own mail server but cannot afford a static IP address or dedicated online presence.