Simple Mail Transport Protocol (SMTP) is the method used to send mail via the internet. Some ISPs supply SMTP servers and some provide Web Based Mail.
With Web Based Mail systems any mail you send will have the ISPs domain name rather than the domain name you own. In order that your mail has a 'FROM' address of your domain you will need a SMTP server.
Most Web Based Mail systems will usually carry advertising from the ISP at the end of any outgoing mail. The only way to stop these advertising messages is to use a SMTP server.
To send e-mail via a SMTP server from your PC, you will need a mail client (or mail program). Mail clients include Microsoft's Outlook and Outlook Express. The mail client communicates with a SMTP to copy the mail from your PC to the SMTP server. The SMTP server communicates with other SMTP servers to send your mail to the recipients mailbox.
SMTP servers are very useful machines. The bad boys of the internet, the spammers, who send millions of junk, unsolicited email every day are always on the look out for insecure SMTP servers that will relay their junk mail. In order to prevent this anti-social practice it was recommended several years ago that anyone using a SMTP server must be authenticated first. SMTP does not have an authentication system. That's why it is the Simple Mail Transport Protocol! However, POP3 has authentication. Therefore, every SMTP server must have associated with it a POP3 server.
For most of our clients a SMTP server is not required. A SMTP server is only required for clients who use ISPs that: