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The usual default service port for SMTP is port 25 and requests on port 110 go to the email POP3 application for receiving and sending email messages.

Each of the services that the machine performs is done by a program. Each program does something called listening on a port.

A port number is actually a number between 1 and 65535 which identifies to the receiving computer what function you want to perform.

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Port Numbers


Sometimes I think of the internet as a kind of black box. I often refer to an old cartoon which shows a scientist writing a huge equation across a blackboard.

The equation covers the left side and right side of the blackboard, and in the middle is the words "and the a miracle occurs."

That's how most people think of the internet. They browse the internet and send email and just assume that some kind of voodoo-like magic sends and receives the information.

Actually, there is about as much magic involved as there is in an engine for a car. The internet is just a huge machine, made up of smaller machines, which are in turn made up of yet smaller machines.

eMail Bolts & Nuts FAQ's
How to manage and clean bounced undelivered emails? Understand why emails get bounced
How to use your desktop PCs as an email server and bypass your ISP email server, a simple process using a free mail server program
How to test your message and see if it gets deleted by broad based anti-spam filters?
A one page email course. Everything you wanted to know about emailing in a "nut shell"
Quick guide to: dig finger traceroute ping whois nslookup IP block FTP SMTP relay TCP/IP Port
How to embed email tracking code into your email? Invisible counters, codes, scripts to track viewer
Send HTML or TEXT email using formatted HTML email, you can send an entire webpage
How to embed images into HTML email for faster emailing? Prevent displaying linked-site in recipient email client status bar
RFC defined ESMTP, SMTP Status Email Error Codes? These codes are used to provide informative explanations of error conditions
How email works?  Delivery of each email is done by your ISP mail server, first establishing a conversation through your recipient port 25
Some spiders visit site after site, collecting email addresses and controlling these rogue spiders spam bots or email harvesters with robot.txt
About TCP/IP and mail server port numbers? It is a number between 1 and 65535 which identifies to the receiving computer what function you want to perform

One of the major components (if you can call it that) of the internet is TCP/IP. If the internet were a body, then TCP/IP would be the nerve impulses which make it do things (that's a very rough analogy, but it will serve).

A TCP/IP number is a set of four smaller numbers, separated by dots, which represent the address of a single machine on the internet.

Every single machine on a TCP/IP network has a unique number which other machines can use to send messages to that machine.

Thus to send, say, a web page to a machine a web server might send it to a TCP/IP address of 167.34.23.1. How does it know where to send it?

The machine which asked for the web page (the user entered a URL in a browser) sent along it's address in the request. The web server merely sends the data back to that address. TCP/IP Transmission Control Protocol / Internet Protocol. The primary protocol used on the Internet.

Here's where port numbers come into play.

Let's say you want to look at a web page and you enter the URL into your browser. This gets sent out to the internet, and through various means winds up at a machine which receives browser requests and returns graphics, web pages and perhaps video and sound.

That machine probably does a number of things. Of course, it handles requests for web pages and such, but it also must send email (using a program called sendmail), receive mail (using POP or Post Office Protocol)....

.... responds to PING requests (a way to determine if a machine is up or has crashed), talk to the name servers so that the internet knows it exist and any of a hundred other things. (Protocol - A method of sending and receiving data)

POP Post Office Protocol rfc1939 used for delivering messages to (client) mail readers  (fetches mails from a remote mail server and stores it locally).

How does the machine know the difference?

The answer is a port number is used. Each of the services that the machine performs is done by a program. Each program does something called listening on a port.

A port number is actually a number between 1 and 65535 which identifies to the receiving computer what function you want to perform.

Your web browser normally makes requests on port 80 (the URL http://msn.com is actually sent as http://msn.com:80, the 80 being the port number).

The receiving machine (the web server) has an application which listens on port 80. When it sees a request on that port number, the machine knows the request should be sent to the web server application.

On the other hand, requests on port 21 are sent to the FTP application, and requests on port 110 go to the email POP3 application.

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Copyright (c) 1999-2001, Richard Lowe Jr And Claudia Arevalo-Lowe. Richard Lowe Jr. is the webmaster of Internet Tips And Secrets. This website includes over 1,000 free articles to improve your internet profits, enjoyment and knowledge.

Learn how to create, promote and maintain an awesome website  which not only attracts visitors but makes them want to come back. You can visit the web site at www.internet-tips.net subscribe to the weekly ezine at www.internet-tips.net/joinlist.htm and subscribe to daily tips by sending an email to internet-tips @ getresponse.com 

Claudia Arevalo-Lowe is the webmistress of Internet Tips And Secrets and Surviving Asthma. Visit her site at http://survivingasthma.com

 

 

 


 

 

eMail Bolts & Nuts FAQ's
How to manage and clean bounced undelivered emails? Understand why emails get bounced
How to use your desktop PCs as an email server and bypass your ISP email server, a simple process using a free mail server program
How to test your message and see if it gets deleted by broad based anti-spam filters?
A one page email course. Everything you wanted to know about emailing in a "nut shell"
Quick guide to: dig finger traceroute ping whois nslookup IP block FTP SMTP relay TCP/IP Port
How to embed email tracking code into your email? Invisible counters, codes, scripts to track viewer
Send HTML or TEXT email using formatted HTML email, you can send an entire webpage
How to embed images into HTML email for faster emailing? Prevent displaying linked-site in recipient email client status bar
RFC defined ESMTP, SMTP Status Email Error Codes? These codes are used to provide informative explanations of error conditions
How email works?  Delivery of each email is done by your ISP mail server, first establishing a conversation through your recipient port 25
Some spiders visit site after site, collecting email addresses and controlling these rogue spiders spam bots or email harvesters with robot.txt
About TCP/IP and mail server port numbers? It is a number between 1 and 65535 which identifies to the receiving computer what function you want to perform

Spam-tracking 103 WHOIS tool nslookup and traceroute freeware download

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whois.internic.net or network solutions are network registries to find out contact info for current domain or IP address

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nslookup a DNS tool that Perform forward and reverse DNS queries for the current address (this will usually give you the IP address of a hostname)

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traceroute finds the route packets take between you and the selected address

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Email in a "nut shell" a one page course about emailing. Everything you wanted to know about emailing.

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How email works? Delivery of each email is done by your ISP mailserver establishing a conversation through (port 25) of your recipient mail server

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Free2-Try 100% effective. The easiest way to Stop Spam getting into your PC. I recommend it.

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Free eBook Sun Tzu Art of War Commanders without thoughtful strategy invite defeat.

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Free eBook Great online Stealth Marketing strategies to help you increase sales

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