| When you type an email address for a message and | | | | information obfuscated. The sending server connects |
| hit send, how does the email know where to go? | | | | to the destination server. It says hello. The |
| Your email client (email software) wraps up your | | | | destination server replies with ELHO. They are even |
| email along with certain information about the | | | | on a first name basis. The sending server says, "I |
| message, and sends the email to your SMTP Server | | | | have a message for one of your people, and it is this |
| (The SMTP server handles outgoing email. SMTP | | | | big." |
| stands for Simple Mail Transfer Protocol) Which SMTP | | | | The destination server looks up the email address, |
| server you use is configured in your email software. | | | | and looks to see if it wants to, and is able to, |
| Most people use the SMTP server provided by their | | | | receive email for the recipient. It then tells the |
| Internet Service Provider (ISP). Or if you use web | | | | sending server. "Ok, send it on" |
| based email such as Hotmail or Yahoo mail, you have | | | | The sending server then says, Ok, I am sending the |
| no control over the SMTP server -- it is built in. | | | | message. You will know when it is done when you |
| Your SMTP server accepts the email, looks up the IP | | | | see two carriage return line feeds (CRLF) back to |
| address of the destination server, breaks the | | | | back. The receiving server then acknowledges |
| message up into packets, and sends the packets to | | | | receipt of the message and the conversation ends. |
| the destination through a series of "hops" (usually a | | | | Connecting to [61.00.00.122]:25 ... connected |
| sequence of very high-powered routers). The path | | | | SMTP (receiving) 220 ESMTP server ready Tue, 23 |
| that your email takes through the internet is | | | | Dec 2008 21:58:40 +0000 |
| determined by the various routers. The routers used | | | | SMTP (sending) EHLO um-232.shxxs.net |
| for internet routing have been compared with | | | | SMTP (receiving) 250- 250-ETRN 250-AUTH=LOGIN |
| supercomputers. They look at various possible paths | | | | PLAIN 250-AUTH LOGIN PLAIN 250-PIPELINING |
| to the destination, and decide the best route to take. | | | | 250-DSN 250-8BITMIME 250 SIZE 15728640 |
| The individual packets may all use the same route, or | | | | SMTP (sending) MAIL FROM: 411.4.600062-12189942 |
| some my go through one path, then the router may | | | | @ (sending) RCPT TO: kxxxy @ bixxd.net |
| decide that there is too much traffic along that path, | | | | SMTP (sending) DATA |
| and send the rest of the packets through another | | | | SMTP (receiving) 250 Sender 411.4.600062-12189942 |
| path, or a variety of other paths. | | | | @ and extensions ( Ok |
| Once all of the packets have been received, the | | | | SMTP (receiving) 250 Recipient kxxxy @ bixxd.net |
| destination server (usually a "POP" server) hooks the | | | | Ok |
| packets back together and places the email in a | | | | SMTP (receiving) 354 Ok Send data ending with |
| special file and waits for the recipient to request their | | | | CRLF.CRLF |
| email. | | | | SMTP (sending) writing message and terminating . . . . |
| The email servers have an actual conversation. As | | | | . . . |
| you can see, below, they are even very polite. This | | | | SMTP (receiving) 250 Message received: |
| is an actual conversation with the identifying | | | | 20081223215845. @ um-232.shxxs. |