Send Email Failed

Why i can send email for online the same domain connection?

I am using this confs:

require("smtp.php");

$smtp = new smtp_class;

$smtp->host_name = "smtp.******.com";
$smtp->host_port = 587;
$smtp->ssl = 0;

$smtp->SendMessage(
"***@***.***",
array(***),
array(
"MIME-Version: 1.0",
"Content-type: text/html; charset=utf-8",
"From: ***@***.***",
"To: ***@***.***",
"Subject: ***",
"Date: ".strftime("%a, %d %b %Y %H:%M:%S %Z")
),
"***"
);

But I can only send email to the same domain i was configured. Different domains can not I submit, is missing some setting? My server requires login and authentication. How should I set?

Yes, usually SMTP servers are configured to only relay messages to different domains if you authenticate with an authorized user. You can do that by setting the variables user and password. Take a look at the test_smtp.php example script.