How E-Mail Travels

December 5th, 2006 by siteadmin Leave a reply »

An e-mail message is first composed by a user inputting characters to form a message that will be sent to someone.   We will say that the e-mail is composed on a desktop with a wired connection to a DSL modem.  When the mail is generated the software used to generate the message will create a header which is similar to the writing on the outside of a regular mail envelope.  This header contains information such as the origin and destination of the e-mail.  The user must input the recipient’s e-mail address so the computer knows where to send the message.  For the remainder of this paper we will use the example of as an example of the recipient.  This e-mail address is a series of characters which identify an exclusive mailbox to a person who can send and receive electronic mail.

Once the composer has clicked the send button, the message will be transmitted to a simple mail transfer protocol (SMTP) server.  SMTP is a protocol used to transmit e-mail between two servers.  Most home users will use their ISP’s (internet service provider) SMTP servers.  For example a Bellsouth customer may use as the SMTP server for their outgoing mail.  The software used to send the e-mail will now upload the message that was put in the outbox when the composer pressed the send e-mail button.  The SMTP server will determine the recipient of the e-mail by searching the header of the e-mail.  The server is able to determine that the e-mail is intended for the person with the username “Bob” who has an account on’s SMTP server.  While humans understand, the SMTP server needs an internet protocol (IP) address in order to understand where to send the message.

The SMTP server sends a request to a domain name system (DNS) server asking for the IP address of’s SMTP server.  An IP address serves as a unique identifier on the internet such as a street address does for physical snail mail.  The server returns an IP address such as  The sender’s SMTP server now connects to the SMTP server at using the IP address and sends the e-mail to the account “Bob” on the server.

Now that the recipient’s SMTP server has the message, it must now send the message on to another server usually being a post office protocol 3 (POP3) or internet message access protocol (IMAP) server.  In our case Bob has a POP3 server to which he must connect to in order to download his e-mail.  Bob’s desktop computer is wirelessly connected to the internet using IEEE 802.11, a packet-radio protocol that is also known as Wi-Fi.  Using this protocol, Bob’s computer is able to connect to his wireless router which is connected to his DSL modem so now he has wireless internet.  His e-mail software is able to download his new e-mails by logging in to his POP3 server account using his username and password.



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