How does the email know where to go?

When you type an email address for a message and hit send, how does the email know where to go?

Your email client (email software) wraps your email along with certain information about the message and sends the email to your SMTP server (SMTP server handles outgoing email. SMTP stands for Simple Mail Transfer Protocol) . in your email software. Most people use the SMTP server provided by their Internet Service Provider (ISP). Or if you use web-based email such as Hotmail or Yahoo, you have no control over the SMTP server as it is built in.

Your SMTP server accepts the email, looks up the IP address of the destination server, divides the message into packets, and sends the packets to the destination through a series of “hops” (usually a sequence of very high-powered routers). The route your email takes over the Internet is determined by different routers. Routers used for Internet routing have been likened to supercomputers. They look at various possible paths to the destination and decide the best route to take. Individual packets can all use the same route, or some can go one route, then the router can decide that there is too much traffic along that route and send the rest of the packets through another route, or a variety of other routes. .

Once all the packages have been received, the destination server (usually a “POP” server) reconnects the packages and places the email in a special file and waits for the recipient to request their email.

The email servers have a real conversation. As you can see below, they are even very friendly. This is a real conversation with the obfuscated identifying information. The sending server connects to the destination server. Say hello. The destination server responds with ELHO. They are even based on the first name. The sending server says, “I have a message for one of your people, and it’s that big.”

The destination server looks up the email address and looks if it wants and can receive email from the recipient. Then it tells the sending server. “Ok, send it”

The sending server then says: Ok, I am sending the message. You’ll know when you’re ready when you see two carriage return line feeds (CRLFs) one after the other. The receiving server then acknowledges receipt of the message and ends the conversation.

Connecting to []: 25 … connected

SMTP (receive) 220 ESMTP server ready Tue, 23 December 2008 21:58:40 +0000

SMTP (send) EHLO

SMTP (reception) 250- 250-ETRN 250-AUTH = LOGIN PLAIN 250-AUTH LOGIN PLAIN 250-TUBERÍAS 250-DSN 250-8BITMIME 250 SIZE 15728640

SMTP (sending) MAIL FROM: 411.4.600062-12189942 @ (sending) RCPT TO: kxxxy @

SMTP DATA (sending)

SMTP (receive) 250 Sender 411.4.600062-12189942 @ and extensions (OK

SMTP (receiving) 250 Recipient kxxxy @ OK

SMTP (receiving) 354 OK Send data ending in CRLF.CRLF

SMTP write message (send) and termination. . . . . . .

SMTP (receiving) 250 Message received: 20081223215845. @

SMTP (send) EXIT

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