Transcript
Basic Computer Networking Briefing Paper—Part 3 of 5 Email Networking 1 Connecting computers
2 Network types and equipment
3 Email networking
4 Global and private IP addresses
5 Network server hardware
Email is a service offered on a client-server network. From Part 2 of this series, you know that a clientserver network is one where a server provides network services to clients, at their request.
Contents How does email work? ....................................... 1
In an email client-server network, there are two types of servers—a mail transmission server (SMTP server) and mail reception server (POP 3 server or IMAP 4 server).
What is an SMTP Server?.................................... 2 What are POP3 and IMAP4 Servers?..................... 2 What is a DNS Server? ....................................... 2 How does email flow from sender to receiver?....... 2 Glossary ........................................................... 2
The reason the sending server and receiving server are different is because the protocol used in sending or receiving is different (SMTP and POP protocols).
How does email work?
Together, the SMTP server and POP server are known as mail servers.
Most people are familiar with sending and receiving email with LotusNotes, Outlook or some other email application. But how is it sent and received 'behind the scenes'?
From the diagram below, you can see that the email system delivers email on a network in much the same way that the postal system delivers letters to your letterbox.
3. Press SEND
3. Post letter 1. Write letter 2. Write address
1. Type email 2. Type address 4. Sender SMTP server
4. Local post office 5. Internet
6. Receiver SMTP server 5. Central post office
6. Addressee post office
8. Read letter
Mailbox
7. Mailbox
7. POP server
8. Read email
An email system delivers emails like a postal system delivers letters
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What is an SMTP Server? The Simple Mail Transfer Protocol (SMTP) server is used to send and distribute emails. The email is encoded in SMTP format from the SMTP server at the sender's end, sent via the internet, to the receiver's SMTP server.
What are POP3 and IMAP4 Servers? The Post Office Protocol (POP) server or an Internet Message Access Protocol (IMAP) server retrieves the mail in the mailbox. Both POP and IMAP have undergone development and are often known by their versions, POP3 or IMAP4.
How does email flow from sender to receiver? When you send an email in your email application (for example LotusNotes), the mail is transferred to the SMTP server that your PC is connected to. Using the IP address (translated from the email address by the DNS server), the email travels via the internet to the mailbox of the receiver in the SMTP server where the receiver’s mailbox is located. The receiver sets his or her email application to check whether mail has arrived in the POP (or IMAP) server, for example, every ten minutes. The POP (or IMAP) server checks the contents of the receiver’s mailbox. It informs the receiver that an email has arrived from the sender. The receiver is now able to open and read the mail from the sender.
Glossary DNS POP server The difference between POP and IMAP is that all POP mails are received on the client side, whereas with IMAP this is managed with a mailbox on the server.
IMAP server Clients who have access to an IMAP server can decide whether to receive mail after viewing the title and sender. This is useful for people who work in a mobile environment and do not want to download unnecessary emails.
What is a DNS Server? The Domain Name System (DNS) server translates email addresses and domain names (such as ricoh.com) into Internet Protocol (IP) addresses. Generally, an email address or a domain name uses words that are meaningful to the addressee, whether for personal or commercial reasons. By comparison, an IP address consists of a series of numbers that are often difficult to remember. An IP address format looks like this: 210.173.216.114. The DNS server has a comparative chart for comparing the address in words (ricoh.com) with the IP address (210.173.216.114). This is then used to create the binary IP address that the network can understand.
Domain Name System. The way that internet domain names are located and translated into IP addresses. IMAP Internet Message Access Protocol. A protocol that allows email messages to be accessed and manipulated on a remote mail server. Email applications commonly use IMAP or POP for retrieving messages and SMTP for sending messages. IMAP is a newer protocol than POP and allows users to manipulate email messages and mail folders on the remote server—without first downloading them to the local machine. Using IMAP, users can create, delete and rename mailboxes, and search, selectively retrieve and delete email messages. POP Post Office Protocol. A protocol that allows email messages to be retrieved from a local server mailbox and downloaded to the recipient’s computer. Email applications commonly use POP or IMAP for retrieving messages and SMTP for sending messages. While SMTP has a limited ability to queue messages at the receiving end, POP was defined specifically to handle email retrieval. The most recent version of POP is POP3. Protocol A special set of rules for transmitting data between two devices. SMTP Simple Mail Transfer Protocol. The standard email protocol on the internet. It defines the message format and the message transfer agent, which stores and forwards the mail.
At all levels, the DNS server simply makes life easier for humans! Prepared by Ricoh Asia Pacific for
Comments? Please send any feedback about this document to:
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Version 0.003, October 2005
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