Some of us may wander what it means to have configured our Email Client (like Outlook or Eudora) for POP3 on port 110? Well, the Internet exists for many years in terms of computer history. In the old days, things were designed with simplicity and "openness for everybody" in mind. People had no time to waist to write viruses. The Internet was meant to be a vehicle for exchanging creative ideas. People were so busy to share their thoughts they used short but cryptic acronyms to name the tools to carry their thoughts. That's why until today we use POP3 and SMTP to receive and send email.

POP3 stands for Post Office Protocol version 3 and is used to handle email between Email Server and our Local Email Client (like Outlook or Eudora). POP3 is used to authenticate our credentials on the server and download email that comes from across the Internet to our email account. Use of POP3 protocol is activated when we click on "Receive" button in our email client. Until this happens our email will stay on the Email Server".

SMTP stands for Simple Mail Transfer Protocol. This protocol is used to deliver email from our Email Client to the recipient's Email Server. The email will stay on the recipient's Email Server until it is explicitly requested to be downloaded by the recipient's Email client over, yes, POP3 protocol. The original SMTP protocol had no authentication built in. Today most of SMTP protocols in use have build in authentication to forbid relying email across domains. This means that for John - whose email address is John@JohnDomain.com -  to send email from his email client he must use the JohnDomain.com Email Server's SMTP service. Yes, it is obvious for most of us. But because in the past the SMTP protocol had no authentication built in this meant that theoretically people who didn't belong to the domain could use the service.

The following diagram has a simplified explanation of how the two protocols are used. Please click on the images to display larger diagram.

Table 1: How email works. A simplified diagram of internet protocols used to send and receive email over The Internet.

Here are some links that give in depth information on POP and SMTP protocols:

If you have questions or would like to contribute to this article please send email to support@applix.net

November, 2004
applix.net support

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