When ever you connect to the internet or go online you are using TCP/IP this is
Transmission Control Protocol (TCP) and the Internet Protocol (IP),
These are different protocols allowing your computer to connect to the internet and to transfer and receive data.

If you use an online mail program like yahoo, Gmail etc, then you are connecting to another computer allowing you to see your email with out downloading it to your computer. This can be very useful because you can access it from any computer and it will not downlaod all of the spam or potential viruses to your computer.
But you are still using TCP/IP
and the Yahoo and Google email servers still have to use SMTP, IMAP, or POP.

If you use Outlook or Lotus or some other email program on your computer then you need to know the SMTP and POP addresses for the email server that you want to access. This would usually be your ISP, internet Service Provider, or your web host if you have a web site. Your ISP or web host has an email server and you get the address from them so that your computer can get connect to their server.
I don't like this option because that you get a lot of spam delivered to your computer and the potential for a virus being loaded to your computer. I just do all of my email through an online web mail program , that way it all stays on their server and not on my computer.

Hopefully that will clear some things up for you.

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Bruce
Artist for Hire - Arts and Webmaster forums