How Mail Server Works

Page 2 : Procedures of Sending and Receiving Emails

The sending and receiving emails are simple but quite interesting. Let’s use an example to discuss how emails are sent and received.

Email Clients Configuration of Sender and Receiver

The following are the setting of Email Clients of both sender and receiver:

Configuration of Netscape Mail Email Client of William:

Email Contents William Send to Us:

Our Netscape Mail Email Client Configuration:

Procedures of Sending Email and Receiving Email

The following diagram shows the procedures that email sending from William (Sender) to MyGreatName.com (Receiver).

We will discuss the procedures of Out-going email and In-coming email one by one.

Out-going Email Procedures:

When William composed the above email and click on the ‘Send’ button, the email begins it's long journey:

1. The Netscape Mail email client of William will contact and connect with Port 25 of configured SMTP Server (smtp.Your_ISP.com) at once.
2. The Netscape Mail inform smtp.Your_ISP.com Server the information of sender and receiver.
3. smtp.Your_ISP.com confirm correct sender information, receive the email, put it in the 'Awaiting Out-Going Mails' list, and waiting to send out.
4. Suppose there are 100 emails awaiting to deliver in the smtp.Your_ISP.com server. Therefore the email William send to us is in the 101 position of the waiting list.
5. The smtp.Your_ISP.com server is very busy in sending out the emails in the waiting list. 100, 99, 98, 97, …… 5, 4, 3, 2, 1. Okay! It’s time to send out the William's email.
6. The smtp.Your_ISP.com server is now handling the email of William. Firstly, the server will break the receiver email address (general@MyGreatName.com) into two parts:
   receiver email account name – general
   receiver domain name – MyGreatName.com
7. The domain name (MyGreatName.com) is for human use only. The computer must get the IP address of MyGreatName.com’s SMTP Server (smtp.MyGreatName.com). In order to get the IP address of smtp.MyGreatName.com, the smtp.Your_ISP.com must first contact Domain Name Server and query the IP address of smtp.MyGreatName.com Server.
8. The Domain Name Server reply the IP address of smtp.MyGreatName.com to smtp.Your_ISP.com Server.
9. Now smtp.Your_ISP.com server has the IP address of smtp.MyGreatName.com server, it can start sending the email.
10. The smtp.Your_ISP.com server now connect with the communication port 25 of smtp.MyGreatName.com, and informing smtp.MyGreatName.com that an email is going to send to him.
11. The smtp.MyGreatName.com server confirm that 'general' is one of the email account under MyGreatName.com. Then it passes the email to MyGreatName.com POP3 server.
12. The MyGreatName.com POP3 server open the ‘general’ email account (general.txt), and append the contents of email to the end. The situation is like:
    ————————-
    ————————-
    ————————-
    From : xxxxxx
    To : general
    Subject : The 20th Email
    Alex,
    xxxxxxxxxxxxxxxxxx,
    xxxxxxxxxxxxxxxxxx.
    Customer
    From : William
    To : general
    Subject : Sign Up
    Alex,
    I like to sign up your service.
    Your service is great!
    William

Up to now, the email that William sent to us has been arrived at our mail box. The procedures of out-going email is also finished.

Now let's discuss the procedures of In-coming email.

Incoming Email Procedures

The email send by William has arrived at our mail box. Let’s see how can we retrieve the email from our mail box:

1. We constantly check if there are any new mails at our mail box. Now Alex click on the 'Receive Mail' button of Netscape Mail.
2. The Netscape Mail email program will connect with the communication port 110 of MyGreatName.com POP3 server at once.
3. The MyGreatName.com POP3 server will request the user name and password. If the information are correct, POP3 server will open the general.txt text file, and download all new emails to the computer of Alex. The contents of general.txt will also be cleared (Of course you can also configure to keep all the emails in general.txt).

Then the whole procedures of sending and receiving emails were completed.