In order to send email through our servers you must authorize yourself to do so. To do this you must checking incoming email first. If you are using Outlook or Outlook Express you can go to Tools > Accounts... > Mail (tab at the top of the new window > Double click on the email account you set up > Click on Servers (tab at the top of the new window, or this may be under advanced properties) > put a check in the box that says "My server requires outgoing SMTP authentication".

If this does not work it is possible that your ISP is blocking outside email servers so that you must use their outgoing email servers. This is done by the ISP in an error to block SPAM. MindSpring, Earthlink,  and AT&T are known to be some ISPs which do this. If your ISP does block outgoing email servers and you are unable to use theirs, you can use the Web Mail feature in your cpanel to send/receive email. Just to go yoursite.com/webmail and log in with your full email address as your username.