3.  Email Client:  What’s that?

The software interface that you (sitting at your computer) use to interact with the Email System (i.e. to compose, send and receive email messages) is an Email Client.

The email client software typically consists of a several components:

Document Editor.

Address Book

Permanent Storage

Communications Module

The Document Editor allows the email user to compose the actual message itself.  Additional features can include a spell checker, formatting facilities and the ability to include files or documents attached to the main message.  An example of an attached file could be a schematic or diagram or even a sound file, allowing the recipient to closely monitor the progress of a project and reply with constructive comments.

The Address Book allows the user to store and organize frequently used addresses in a convenient format, greatly reducing the chance of addressing errors.

Permanent Storage stores sent and received email messages allowing for efficient record keeping of communications.  The ability to sort and search archived messages by date, addressee or subject is an added convenience.

The Communication Module is the heart of the Email Client software.  Although it is not seen, it works under the covers to send and receive the messages and attachments, negotiating with networks, the internet and other email clients for the smooth transmission of your important information.  A more detailed treatment of how this communication actually occurs is handled chapter.

4.  What does the Mail Server do?

The Mail Server is the heart of any email system.  It is the application that receives mail from the email client and from other mail servers.

The typical components of a mail server are:

Permanent Storage

User Defined Rules

Mail Server Users List

Communications Modules

Permanent Storage is where incoming mail is stored for later distribution to local users.  Messages that are in transit to other destinations are also temporarily stored here.  The typical structure of the storage area is that of a simple database.

User Defined Rules determine how the Mail Server deals with directing incoming messages to their destinations and also how it reacts to the sender of the message.  Rules can be used to bar some senders from delivering mail to local users or to limit the types of messages local users can send and to whether they can send messages outside of the local network.

The Mail Server Users List is a database storing the names of local users that it will recognize and deliver incoming mail to.

The Communications Modules are the components that handle the transfer of incoming and outgoing messages to and from local users and other mail servers.  The complexity and number of modules is dictated by the needs of the email system.  A detailed discussion of communication modules will follow later.

The system administrator for an email system is often referred to as the “Postmaster.”  The Postmaster is responsible for maintaining the list of users associated with the system and also establishes the Rules.

The operation of most Mail Servers is automatic.  The Mail Server waits to receive local messages or messages from other mail servers and then processes/delivers them according to the established Rules. 

5.  Basic Email Systems & How They Work:

The following four examples will illustrate several types of simple network based email systems and the way they communicate internally and with outside systems.

5a.  Simple Office Email System

If communication is required within an office but not to the rest of the outside world then a simple email system could be set up for effective “inter-office” email communication.

In this simple example: three users known as “Eric” “Barry” and “Irene” are connected via a computer network within their company office.  If one of them wants to send a message to another they would simply type their message and send it to the company’s mail server addressed with the “email name” of their intended recipient.  In our example the email name is simply the user’s first name (i.e. Eric.)

A sample communication would go as follows:  Eric wants to send a message to Irene; he types it out on his Email Client and addresses it to Irene.  His Email Client then forwards the message to the Mail Server, where it is stored for Irene.  The next time Irene uses her Email Client to check for and retrieve any pending messages, Eric’s message will a forwarded to her and she can read it an respond if necessary.  In such a simple and small system recipients need only be identified by their name.

The flexibility of such a system could be greatly increased if some form of connectivity is added to the network via a modem (a modem transmits computer commands over telephone or cable lines, making this connection a part of the computer’s network.) We will see this in our next example.

5b.   Office email accessible to remote users

Allen works from home.  When Allen wants to send a message to Barry he types it out within his Email Client and at his discretion his Email Client dials (via a telephone or cable modem) into the company’s computer network, delivers Allen’s message for Barry and retrieves any waiting messages.  Once the messages are collected the modem disconnects and Allen is free to read the retrieved messages.

Since Allen’s computer is communicating via the phone lines, he can retrieve messages from any location he has access to a telephone jack.  Other remote company employees can also do the same and even send messages to one another via the telephone system linked through the company network and mail server just as easily as they would to any user physically connected to the network.  Compared to traditional paper memos and telephone messages, the flexibility and advantages of an email system becomes clear.

In our next example we will see how messages can be sent to another office or company.

5c.  Simple email communication between offices

In this example, two offices have simple email communication via modems and  telephone lines.

Email messages are generated and sent internally much as we have discussed earlier.  However, since the destination is to a different site, the addressing of the message is more complex.  As we see in this example each office has an Eric to which an email can be sent.  How can a message be addressed to a specific Eric?  There are two way to address your meassage:

1.  Have Eric at the Local Office change his email name to something else.  A common method is to add the initial letter of the email user’s last name (i.e. we would use the “J” from Eric Jones’ last name to create the user name of “Eric.J”)  Although there is no standard “user name” convention to adhere to, try to use a rule that is simple to remember, creates short names and will be implemented throughout the company uniformly.

2.  Users could also be identified by the addition of a second piece of information in their “user name”.  In this instance the specific office (or site) could be a unique identifier.  To send mail to Eric at the Main Office you might address the message “Eric@main.office”.  Please note the @ symbol is used to indicate a location and also note there are no spaces used within an email “user name” or “address.”

Method 2 is prefered since it allows for future expansion of the company with the addition of new local offices which could have location addresses such as “local.office.A” or “local.office.B”.  In the real world more descriptive addresses such as “NewYork.office” and “Huston.office” might be used.  These user name components are know as “Domains”; they specify the location within a company of the specific user.  (These are not to be confused with “Internet Domains”; these are internal company domains.)

A system like the above can also be accessed by remote users allowing for a very comprehensive and flexible company email system.

The types of sytems we have examined so far are limited to email communication within a company.  Our next example will show how the public Internet can be used for email communication.

5d.  A single user dialing into an Internet Service Provider (ISP)

When a home user connects to the Internet via their Internet Service Provider (ISP) they are using the ISP’s network just as we saw previously in example 5B.  The only difference is that the ISP’s computer network is itself connected to the Internet.  To prevent bottleneck, the ISP will usually have a large number of modems to support their users.

The home user simply connects via modem to retrieve his or her email messages. These messages are stored on the ISP’s mail server, and to send any outgoing messages, they are uploaded to the ISP's mail server for later transmission. The user then disconnects just as in the example of a simple company’s email system.

Again as in our previous example, addresses are the most complex aspect of email communication.  Because the Internet is a vast and ever increasing number of smaller networks, the email address must specifically define the recipient’s Domain.  As you can imagine the quantity of Eric’s on the Internet could be staggering!

More on Domains: Each network connected to the Internet has its own unique Domain name.  This ensures that email and other traffic is directed to the intended recipient.  In our current example the ISP has its own Domain name which directs email messages for a specific user belonging to their Domain to their mail server.

For example, if the ISP is called “EarthLink” they could own a Domain on the Internet called “EarthLink.net”.  Mail to our home user would be directed to “home.user@EarthLink.net” resulting in the mail being stored on EarthLink’s mail server awaiting the “home user’s” client to collect it.

A remote office worker could also use the same system to collect and send his email via the ISP without ever having to connect to his own company’s internal network.

6.  What is an Email address?

A typical email address could look like the example below:

The address is composed of two parts:

Email Account - This is the “user name” of the account holder that the “tekguard.com” mail server would deal with.

Domain Name - This is the officially name that a company registers and has the right to use within the Internet.

Other recognizable examples of Domain Names are:  yahoo.com, microsoft.com, hotmail.com.

If an individual email user or even a company have not registered their own Domain Name, they could be using the Domain Name of their Internet Service Provider (ISP) for email exchanges.  Perhaps you know of someone with an email address having the Domain Name of: aol.com or netcom.com.  Using someone else’s Domain Name can be a very cost effective means of having email access through the internet; of course the understanding is that you or your company are limited to the exclusive use of the ISP’s Domain Name.

In the example above,  “tekguard.com” is the Domain Name officially registered by VINFO's TekGuard for their exclusive use on the internet.

Additional information about registering Domain Names is available in the Reference URL’s section at the end of Section 2.

7.  How is email transferred from one Email Client to another?

 

The above example illustrates how email messages are transferred between email clients within an office.  Lets analyze the specific steps in the process labeled a, b, c & d:

a)  Let's say Irene wants to send an email message to “barry@company1.com”.  Irene uses the email client on her machine to compose and then send the message to the company’s Mail Server.

The Mail Server checks to see if it has an account by the User Name of “Barry”.  If such an account exists then the Mail Server will store the message in its retrieval queue awaiting Barry’s Email Client to contact the Mail Server and collect the message.  If there is no account for Barry on file then the message will be returned with an explanation that Barry doesn’t have an account and the message couldn’t be delivered.

b)  At some later time, Barry checks his email.  His Email Client contacts the Mail Server and queries it if there are any outstanding messages stored there for Barry.

c)  Since there is a message waiting for Barry from Irene, his Mail Client downloads the message from the Mail Server.  Barry can then use his Email Client to read Irene’s message and compose a response if he so desires (as in process A).

d)  Barry’s response to Irene would be accessible to her after her own Email Client contacts the Mail Server (as in process B).

Let’s say Irene had addressed her message to “eric@company1.com” instead of “barry@company1.com”, and since Eric does not have an email account registered on the Mail Server, Irene would have received a message back from the Mail Server telling her that Eric in not registered as an account holder on the Mail Server and that her message could not be delivered.

8.  How does email get from one Email Client to another at a different location?

Let's say Irene wants to send an email message to across the world to “mark@company2.com” at a completely different company.

a)  Irene creates the message on her own Email Client, which then sends the message to the Mail Server at Company1.

b)  The Company1 Mail Server compares the destination’s Domain Name (company2.com) against the Domain Name it normally administers (company1.com).  Since the Domain Name is different the Company1 Mail Server will transfer the file to the Mail Server responsible for messages addressed to “company2.com” domain.  Note:  the process by which the Company1 Mail Server locates and communicates with the Company2 Mail Server will be discussed later.

c) At a later time, Mark checks his email for new messages.  His own Email Client contacts the Mail Server at Company2 and queries if there are any pending messages stored there for Mark.

d) Since there is a message waiting for Mark from Irene, Mark’s Email Client downloads the message from the Company2 Mail Server.  Mark can read the message on his Email Client and compose a response if so desires.

e)  Irene would receive her response from Mark if checked the Company1 Mail Server for new messages with her Email Client (as in process C).

Let’s say Irene had addressed her message to “eric@company2.com” instead of mark@company2.com. Since Eric does not have an email account registered on the Company2 Mail Server; Irene would have received a message back from the Mail Server telling her that Eric in not registered as an account holder on the Company2 Mail Server and that her message could not be delivered.

9.  What if a destination Mail Server cannot be found by the sending Mail Server?

Occasionally the destination Mail Server is unavailable either because it is extremely busy or cannot be found at all.  Such a situation can result in a number of different outcomes:

In the circumstance that the sending Mail Server cannot find any information about the destination, then the sender is notified that his message was not delivered and why it failed.  Very often the message was mis-addressed.  Most mis-addressing is result of a simple misspelling in either the Email Account or Domain Name portions of the email address.

In the case that the sending Mail Server can find some information regarding the Domain of the destination Mail Server it is attempting to contact, but is unable to make contact with the destination Mail Server, the sending Mail Server will hold the message for a specified period of time and then try to deliver the message again.  If after a number of attempts the sending Mail Server is still unsuccessful in delivering the message then it will return the message back to the sender’s Email Client with a message that it tried to deliver several time but ultimately failed.

This type of partial communication will occur if the destination Mail Server is unavailable for some reason (i.e. it is on a part time connection or the system has crashed.)

To safeguard against such a failure in email communication, very often another Mail Server will also be assigned to look after a specific Domain.  So if the primary destination Mail Server cannot be found then the alternate Mail Server can accept mail on its behalf.  Such a redundancy scheme can be designed to include a great number of Mail Servers.  Should no Mail Server be available to accept the email message then the sending Mail Server will wait a predetermined period of time and try to send the message again.

Larger organizations will often have 10 or more Mail Servers looking after their Domain; each server passing the email messages on to the final destination Mail Server.

Such a strategy allows continued email service when the primary mail server is extremely busy, as in the case of large ISP’s that handle many thousands of email communications in a single hour.