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How Mail Server Works

Page 1 : Knowing SMTP and POP3 Mail Severs

Have you ever wonder how Mail Server works? Why we have to configure the email clients in order to send and receive emails? What are the SMTP and POP3 in the configuration fields of email client? Let’s discuss this topic.

SMTP and POP3 Mail Severs

Mail servers are actually not too complicated. This article provide some basic information you may wish to know.

Basic Concept of Mail Servers

The sending and receiving emails are handled by Mail Servers. Actually a Mail Server compose of two separate servers. These two servers are responsible for different tasks. These two servers are:

  • SMTP Server – mainly handling Out-going (Sending) emails
  • POP3 Server – mainly handling In-coming (Receiving) emails

Out-going emails are emails sending from your computer to your friend’s email address.

In-coming emails are emails sending from your friend to your computer.

The following is a schematic diagram of a Mail Server:

Mail Server Structure

Let's discuss the SMTP and POP3 Mail Servers one by one.

SMTP Mail Server

SMTP (Simple Mail Transfer Protocol) is a communication protocol used to handle the sending and receiving of emails. A Mail Server can handle emails when it install SMTP.

Suppose you are now using an email client (e.g. Netscape Mail, Internet Mail, Outlook, etc.) to send an email. After you click on the 'Send Mail' button, the email client program will contact the configured SMTP Server (e.g. Your ISP Mail Server which is usually like at once. When the configured SMTP Server detect signal of Port 25 (knocking door), it will 'open the door' and chatting with the email client program, for example:

SMTP Server: Please to meet you, I am…..

Email Client Program: I need to send an email to…… from….

SMTP Server: Hm…..

When the identity of the email client has been confirmed, the SMTP Server will receive the email, put it in the queue of the 'Awaiting Out-Going Email List', and waiting to send out.

The queuing time to send the email depends on the quantity of emails handling by the SMTP Server. However the time will usually be very short.

When the time come to send your email, the SMTP Server will contact with the SMTP Server of receiver. The receiver SMTP Server will also 'open the door' and chat with your SMTP Server. When the identity of sender is confirmed, the receiver SMTP Server will receive the email, and put it in the POP3 Server under the receiver account.

POP3 Server

POP3 (Post Office Protocol) is a very simple stuff. It simply use to save a lot of text files. Each text file is actually an email account. For example, if your email user name is william, there is a william.txt text file in the POP3 Server. If the user name of your email account is patrick, there is a patrick.txt text file in the POP3 Server.

Let’s take the email account william as an example. Whenever the email account of william receive new emails, the new emails will append to the end of william.txt text file. If william do not receive and read the emails, the new emails will continue to append to the end of william.txt text file.

Sometime the email client of william request to receive emails. After clicking on the 'Receive Mail' button, the email client program will contact the POP3 Server at once. The POP3 Server will ask the client to enter the user name and password. If the information are correct, the POP3 Server will open the william.txt text file. Therefore william can handle the incoming emails.

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