Problems when using SMTP to send emails

Below is a php example program (adapted) that uses smtp to send emails directly, but the server always prompts: 550 system busy! The email cannot be sent.
Who knows how to deal with it?
What should I do if the smtp server requires a password?
Sory, I just saw the smtp mail sending problem (why isn't this post linked to the essence ?, We recommend that you give it one ).
The problem has been solved:
1. The data command should be "DATA"
2. The from and to commands should be available; otherwise, some servers reject emails.
3. Use base64_encode to encrypt the user name and password
<? Php
Require ("phpmail. php ");
?>
<?
$ Smtp = "smtp.163.net ";
$ From = "hylpro@163.net ";
$ To = "hylpro@163.net ";
$ Subject = "Hello php mail ";
$ Message = "Hello! This is a test use php ";
$ Mail = new mail ($ smtp, "Welcom use this mail", true );
$ Mail-> send ($ to, $ from, $ subject, $ message );
?>

<?
//---------------
// Implement SMTP
//---------------
Class Mail {
Var $ lastmessage; // record the last response
Var $ lastact; // The final action, in the string format
Var $ welcome; // used after HELO. welcome
Var $ debug; // whether to display debugging information
Var $ smtp; // smtp server
Var $ port; // smtp port number
Var $ fp; // socket handle
// Construct
Function mail ($ smtp, $ welcome = "", $ debug = false)
{
If (empty ($ smtp) die ("SMTP cannt be NULL! ");
$ This-> smtp = $ smtp;
If (empty ($ welcome ))
{
$ This-> welcome = gethostbyaddr ("localhost ");
}
Else
$ This-> welcome = $ welcome;
$ This-> debug = $ debug;
$ This-> lastmessage = "";
$ This-> lastact = "";
$ This-> port = "25 ";
}
//
Function show_debug ($ message, $ inout)
{
If ($ this-> debug)
{
If ($ inout = "in") // response information
{
$ M = "<B> accept: </B> ";
}
Else
$ M = "<B> hair: </B> ";
If (! Ereg ("n $", $ message ))
$ Message. = "";