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How Email Works
There is much more to email than
meets the eye. We provide here, some background information
about email and how it works, and a simple step-by-step
diagram showing how an email message is sent and received.
What is an email client?
An email client is an email program such as Outlook Express,
for sending, receiving and organizing your email messages.
What is an email server?
Email servers are used to process, store and send, and receive
email messages. There are different types of email servers,
such as POP 3, SMTP and IMAP servers. The most popular email
servers are POP 3 (incoming mail servers for your incoming
mail) and SMTP (outgoing mail servers for your outgoing
mail).
What is SMTP or outgoing
mail server?
When you send an email from your email program, if you have
an Internet connection with Comentum, the email first arrives
at our SMTP (outgoing mail server), then our SMTP server
will check for the validity of both source and destination
email addresses. Then it will send your email to the proper
destination. You use your Internet conection’s email
server when you send mail.
What is POP3 or incoming
mail server?
When someone sends you an email message, it arrives at our
POP3 server and it waits for you to check your email. When
you check your email, your email program accesses our POP3
servers and downloads your waiting messages from our POP3
server to your computer.
What is Web Mail?
Sending and receiving email messages using a web browser
is referred to as "Web Mail." Using Web Mail is
ideal when traveling or using another person’s computer
or an outside computer, such as at the library or at a trade
show. You can access Comentum's Web Mail as long as you
have a browser and an Internet connection. You can always
use Comentum's Web Mail in conjunction with your usual email
program, such as Outlook Express.
What is the difference between
Web Mail and Client Email (such as Outlook Express)?
Client email, such as Outlook Express will ordinarily download
and save your messages to your computer, and then it deletes
your email messages from our servers. Comentum's Web Mail
will not download and save your messages to your computer;
it will leave your messages on our servers, unless you manually
delete them.
How does email travel when
I receive or send an email message?
When Lisa sends Bob an email message (Figure B), the following
is a simplified step-by-step of how it travels:
1. Lisa opens her email program (Outlook Express), uses
her email account, lisa@otherisp.com, and writes an email
message to bob@comentum.com. Her Outlook Express sends the
message through TCP port 25 of Lisa’s Internet connection,
then to the other ISP’s SMTP server (still on TCP port
25).
2. The other ISP’s SMTP server finds the destination’s
SMTP server (in this case, Comentum) and sends the message
out to Comentum’s SMTP server (through TCP port 25
of her Internet connection).
3. Comentum’s SMTP server sends the message to Comentum’s
POP3 server where the message waits for Bob to pick it up.
4. Bob opens his email program (Outlook Express) and when
he clicks Send/Recv button, his Outlook Express sends a
request through Bob’s Internet connection to Comentum’s
Pop3 server (through TCP port 110) and downloads Bob’s
message to Bob’s computer where he sees Lisa’s
message.
The same process happens in reverse, when Bob sends Lisa
an email message (Figure A on the front).
* There are other network elements that are necessary to
make this process happen, such as: Comentum’s routers,
Comentum’s DNS servers and Comentum’s Internet
connection, and other ISP’s routers, DNS servers and
Internet connection. We left those elements out and concentrated
on email clients and email servers.
** Bob may use a different ISP for his Internet connection
and to host his domain, website and email (bob@hiscompany.com.)
Bob@hiscompany.com uses the same Comentum mail servers described
in Figure A and B..
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Sendng Email
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Receiving Email
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