使用ini_set（）从php.ini进行邮件设置

I'm having a problem regarding with the custom ini_set() for Mail settings. The problem is that somehow my PHP server does not detect the custom ini_set() just like below.

ini_set('SMTP','mail_Server.com'); // the custom server that I want to use
ini_set('smtp_port','465'); // custom port according to the server mail
ini_set('sendmail_from','send@mail.com'); // email use to send the mail

$recipients = array(
    "email@1.com",
    "email@2.com");
$f_to = implode(',', $recipients); // recipients email address

$subject = "subjects";
$body = 'body content';
$body.= 'message content';
$headers = "From send@mail.com";


mail($f_to, $subject, $body, $header); // email sent

The code work just fine and the script did sent me an email, but not from the custom server that I want it to. Instead it sent the email according to default settings from php.ini.

I appreciate any help or comment regarding to this matter. Thanks!