I think I have everything set up right but when someone tries to register they get the message about New User Account Created...you will recieve an email in the next few seconds to activate your account deal....but above all it it shows an error:

Warning: mail(): SMTP server response: 551 User not local. Authentication required for relay in c:\appserv\www\modules\Your_Account\index.php on line 146

And they never recieve an email to activate the account. How can I fix this as I don't know much about SMTP. Thanks for any help.