ciw lesson 7
E-mail on a network E-mail works on a network much as it does over the Internet. Each user has a specific IP address within the company's domain, and messages are routed from one user to another via the network server, which uses TCP/IP to transfer messages to specific IP addresses. However, LANs may use proprietary protocols to send messages to people within the LAN, and use SMTP to send e-mail to recipients outside the LAN, such as remote employees or business associates. Some networks may be self-contained; they will use only proprietary protocols to send messages to people within the LAN. You may be unable to connect to the global Internet from within your company's network. In such cases, you can send and receive messages to and from your co-workers, but you cannot exchange messages with anyone outside the network.
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E-mail protocols: As you learned earlier in this course, e-mail involves two mail servers: outgoing and incoming. You can use separate servers for outgoing and incoming e-mail, or a single server for both tasks. The outgoing and incoming servers use various protocols to send, receive and store e-mail messages. Outgoing mail protocol: Simple Mail Transfer Protocol (SMTP) You send e-mail to others with an outgoing server using Simple Mail Transfer Protocol (SMTP). SMTP is the Internet standard protocol for transferring e-mail messages from one computer to another. It specifies how two e-mail systems interact. SMTP is responsible solely for sending e-mail messages, and is part of the TCP/IP suite. MTAs and MDAs An outgoing mail server runs a Message Transfer Agent (MTA), also called a mail transport agent, which routes, delivers and receives messages, usually via SMTP. A Mail Delivery Agent (MDA) receives the messages delivered by the MTA and then delivers each message to its proper destination (or mailbox), where a user can pick it up. Incoming mail protocols: POP3 and IMAP As you have learned, you receive e-mail from an incoming mail server using Post Office Protocol version 3 (POP3) or Internet Message Access Protocol (IMAP). POP3 and IMAP are used to store and access e-mail messages.
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Internet Message Access Protocol (IMAP) An IMAP server receives and holds your messages. When you log on with your user name and password, you can read a message on the server, or you can view just the heading and the sender of the message and decide whether to download it. Messages are not downloaded automatically as they are with a POP3 server. E-mail clients, including Mozilla Thunderbird and Microsoft Windows Live Mail, support IMAP and allow you to specify multiple IMAP accounts. Using IMAP, you can create and manipulate mailboxes or folders directly on the server, and the messages remain on the server until you delete them. IMAP can be thought of as a remote file server. If you are working remotely, you must have a constant connection with the server, and IMAP is more widely used by people who maintain a constant connection, for example through a wireless carrier, DSL, a mobile hotspot or cable. Users who want to work with their e-mail files locally must download their messages.
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Networks and addresses: As you learned previously in this course, Internet communication is made possible by TCP/IP software. Remember that TCP enables two computers to establish a communication link and exchange packets of data, while IP configures the format and addressing scheme of the packets. TCP/IP software sends information to the computer with which you are connected, which then passes it on to other computers until it reaches the destination. Every device on the Internet has a unique IP address, just as every house and business has a street address. An IP address is a series of numbers divided into four sections, each separated by a period, or dot. IP addresses are also called "dotted quads." Local area networks (LANs) and wide area networks (WANs) use IP addresses to identify each user on the network, whether or not the network has access to the Internet. When you log on to the company network, you enter a user name that the network associates with your IP address. Some companies devise their own internal IP address scheme and never connect to the Internet. These companies use TCP/IP across leased lines and establish an internal network. E-mail is available to anyone who has an IP address either on an internal network or on the Internet. When you use e-mail at work, your IT department assigns you an IP address and user name by which the company network recognizes you. Usually when you log on to a company network, you must also enter a password. IT departments generally assign a generic password to a new account, which you can later change. When you purchase Internet service through an ISP or a commercial online service, your provider assigns an IP address to you. Your provider uses that IP address to recognize you, and you can send and receive e-mail using that address. When you are logged on to the network or connected to the Internet, you can create an electronic message using an e-mail program, and send your message across the network (or the Internet) using a specific address for your intended recipient. The network delivers your message, and your recipient receives and reads your message using an e-mail program.
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E-mail services and programs: Many types of e-mail services are available. You can use an e-mail client to send messages over the Internet if you have an account with an ISP. Mozilla Thunderbird is a popular e-mail program on the Internet because it can run on multiple platforms, such as Apple OS X, Linux and Windows. E-mail clients are for e-mail purposes only; however, they are sometimes integrated within a Web browser (Opera Mail is an example of this configuration). An e-mail client is also referred to as a Mail User Agent (MUA). Free e-mail applications: You can also use browser e-mail programs. E-mail applications such as Mozilla Thunderbird, Windows Live Mail and Opera Mail have been available for years. These applications lack sophisticated features found in applications such as Microsoft Outlook, but are appropriate for many individuals and small businesses. Web-based e-mail You can also use Web-based e-mail services. Several such services are available, including Google Gmail, Yahoo! Mail and Outlook.com (formerly Hotmail). Web-based e-mail is free, offers e-mail accounts that are accessible from any computer with Internet access, and permits family members who share a single Internet account to have separate e-mail addresses. However, you must have Internet access through a service provider before you can use Web-based e-mail, or you can use a public computer that offers Internet access, such as a computer at a public library. Web-based MUAs store e-mail messages on their cloud servers, and users access their e-mail through a Web page. You can also use an e-mail client to download mail from a Web-based account. When you create a Web-based e-mail account, you request a user name (e-mail address), and the hosting service will accept or deny your request depending upon whether that name is already in use within that domain. You created a Google account and a Microsoft account earlier in this course. Both accounts provide free e-mail services.
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Electronic mail, or e-mail, is widely embraced for business communication. The commonplace use of electronic mail has given rise to the term snail mail, which is a slang term for the standard postal service. E-mail allows businesses to communicate quickly and efficiently with customers and employees. E-mail is not dead With the advent of texting, many mobile phone users have questioned the usefulness of e-mail. However, e-mail is still the de facto standard communication tool for business. The benefits of using e-mail include the ability to include attachments; the ability write lengthy messages; and having a paper trail, or e-mail thread, of your communications. The ability to easily store and organize e-mail is another major benefit. Messages can quickly be searched, accessed and archived. This is particularly important if you need to find a message from a customer from several years past, for example. Texting is often used between employees for sending quick messages and alerts. For instance, if an employee is meeting with a customer, the parties may text one another about their current location or if they are running late. However, you would not send a business contract using a text message. Texting can be an alternative to e-mail in business, but it is not a replacement.
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Gateways The people sending you messages need not be in the same domain, nor does it matter which e-mail programs they use. Your unique Internet address ensures that the message will be delivered to you. Gateways between e-mail systems allow users on different e-mail systems to exchange messages. A gateway is a computer that connects two networks that have different protocols. Gateways enable you to send and receive e-mail between all Internet mail services over the Internet because they enable different networks to communicate. For example, if you have an account with Google, you can send an e-mail message to your brother in another state, who has an account at his university. He in turn can forward your message to your cousin in another country, who has an account with her employer.
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How E-Mail Works: Whether your e-mail system is configured for you at work or you set up your own system at home with a modem and an e-mail program, the basic function of e-mail is simple: You use it to send electronic messages from one computer to another. For messages to be sent from one computer to another, the computers must be linked, or networked. You may have a physical connection (such as a cable) between the two computer stations, or the computers may each connect to a local server that relays the messages, or the computers may use the Internet to relay messages. Even if you use a Web-based e-mail service such as Gmail, Outlook.com (formerly Hotmail) or Yahoo! Mail (instead of a desktop-based client), the e-mail message is sent from one computer to another. For example, a Gmail server sends an e-mail to an Outlook.com server. The user then downloads the message to his or her PC or mobile
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MIME, S/MIME, PGP and GPG MIME controls the way that messages and attachments are organized and distinguished from one another, whereas S/MIME controls the way that encryption information and digital certificates can be included as part of an e-mail message. Most browsers support S/MIME. PGP and GPG are alternatives to S/MIME. Multipurpose Internet Mail Extensions (MIME) Multipurpose Internet Mail Extensions (MIME) is a protocol that was developed as an extension of SMTP. MIME allows users to exchange various types of data files over the Internet, such as audio, video, images, applications and so forth. MIME is a system that identifies attached files by type. MIME types are classified under broad headings (text, image, applications, audio and video) and then subclassified by specific type. For example, a QuickTime video is identified as a video/quicktime MIME type. Servers insert a MIME definition inside the HTTP header at the beginning of any Web transmission so that your browser (or e-mail client or any other Internet client) can select the appropriate player (whether built-in or plug-in) for the type of data indicated in the header. Modern e-mail clients support MIME, allowing users to receive various types of files as attachments to e-mail messages. When a user opens the attachment, the appropriate application (as specified by the attachment's MIME type) is opened and the attachment can be viewed, heard or otherwise experienced, assuming that the client computer has the appropriate application installed.
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Secure MIME (S/MIME) Secure MIME (S/MIME) is a version of the MIME protocol that provides a secure method of sending e-mail. S/MIME supports encryption and the use of digital certificates in e-mail. (Encryption will be discussed in detail in a later lesson.) Pretty Good Privacy (PGP) An alternative to S/MIME is Pretty Good Privacy (PGP), a method developed by Philip Zimmerman for encrypting and decrypting e-mail messages. PGP is available in a free version defined by the IETF's OpenPGP specification, which uses non-patented encryption algorithms. The commercial version, owned by Symantec Corporation, uses various encryption algorithms, depending on the task. PGP uses the public-key encryption system. Each user has a publicly known encryption key, which is used to encrypt messages, and a private key (known only to that user), which is used to decrypt messages. When you encrypt a message intended for your recipient, you encrypt it using his or her public key. When the recipient receives the message, he or she decrypts it with his or her private key. To use PGP, you download (or purchase) it and install it on your computer. Then you register the public key that your PGP program gives you with a PGP public-key server. This process enables people with whom you exchange messages to find your public key and use it for encrypting messages they send you. PGP runs on most operating systems. You can access the latest free, open-source version from the PGP Alliance's Web site at www.openpgp.org
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To send and receive messages, you need an e-mail address. E-mail addresses use the following format: username@domain All e-mail addresses contain the @ symbol between the user name and the domain. The @ symbol means "at." The following is a typical e-mail address format: [email protected] The part of the address before the @ identifies the user within a domain. The user name is also known as an e-mail account. When you purchase Internet service or when you join a company that has e-mail, you choose (or you are assigned) a user name. Because the rules for creating user names are flexible, conventions vary. Typically, the user name is related to the person's name or job function, as shown in the following examples, and may also include periods, underscores or numbers in addition to letters,: [email protected] [email protected] [email protected] [email protected] The part of the address after the @ is the domain name of the organization or company that issues the e-mail account. (As you learned earlier in this course, a domain name is an IP address represented in words.) The domain name portion of your e-mail address identifies your location on the Internet (or on the company network) so that you can receive mail Your e-mail address, like your home address, is unique; no one else can have the same address within the same domain. For example, different individuals can have the addresses [email protected], [email protected] and [email protected] because the user name is not duplicated within the same domain. This arrangement is similar to having a 1234 Main Street in various U.S. cities.
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