how send email using zend php?

what needs to be done to send email from zend php server?

The following code fails with message "failed to locate mailserver at
mail.company.com

I am able to send mail from the ibm i using QTMMSENDMAIL API.
Meaning the mail server framewok is running?

here is the PHP code I am running. thanks,

<?php
$serverUrl = 'mail.company.com' ;
$smtp_port = 25 ;
$fromMail = 'is_dept@xxxxxxxxxxx' ;
$toMail = 'target@xxxxxxxxx' ;

ini_set("SMTP", $serverUrl) ;
ini_set("sendmail_from", $fromMail ) ;
ini_set("smtp_port", $smtp_port ) ;

$message = "this mail message sent from IBM i" ;
$headers = "From: " . $fromMail ;
mail( $toMail, 'test subject', $message, $headers) ;

echo "check mail. message sent." . "<br>" ;

?>