SMTPconfig.php
You have to change SMTP server details.
<?php
//Server Address
$SmtpServer="127.0.0.1";
$SmtpPort="25"; //default
$SmtpUser="username";
$SmtpPass="password";
?>

SMTPclass.php
SMTP mail sending class.
<?php
class SMTPClient
{

function SMTPClient ($SmtpServer, $SmtpPort, $SmtpUser, $SmtpPass, $from, $to, $subject, $body)
{

$this->SmtpServer = $SmtpServer;
$this->SmtpUser = base64_encode ($SmtpUser);
$this->SmtpPass = base64_encode ($SmtpPass);
$this->from = $from;
$this->to = $to;
$this->subject = $subject;
$this->body = $body;

if ($SmtpPort == "")
{
$this->PortSMTP = 25;
}
else
{
$this->PortSMTP = $SmtpPort;
}
}

function SendMail ()
{
if ($SMTPIN = fsockopen ($this->SmtpServer, $this->PortSMTP))
{
fputs ($SMTPIN, "EHLO ".$HTTP_HOST."\r\n");
$talk["hello"] = fgets ( $SMTPIN, 1024 );
fputs($SMTPIN, "auth login\r\n");
$talk["res"]=fgets($SMTPIN,1024);
fputs($SMTPIN, $this->SmtpUser."\r\n");
$talk["user"]=fgets($SMTPIN,1024);
fputs($SMTPIN, $this->SmtpPass."\r\n");
$talk["pass"]=fgets($SMTPIN,256);
fputs ($SMTPIN, "MAIL FROM: <".$this->from.">\r\n");
$talk["From"] = fgets ( $SMTPIN, 1024 );
fputs ($SMTPIN, "RCPT TO: <".$this->to.">\r\n");
$talk["To"] = fgets ($SMTPIN, 1024);
fputs($SMTPIN, "DATA\r\n");
$talk["data"]=fgets( $SMTPIN,1024 );
fputs($SMTPIN, "To: <".$this->to.">\r\nFrom: <".$this->from.">\r\nSubject:".$this->subject."\r\n\r\n\r\n".$this->body."\r\n.\r\n");
$talk["send"]=fgets($SMTPIN,256);
//CLOSE CONNECTION AND EXIT ...
fputs ($SMTPIN, "QUIT\r\n");
fclose($SMTPIN);
//
}
return $talk;
}
}
?>

index.php
<?php
include('SMTPconfig.php');
include('SMTPClass.php');
if($_SERVER["REQUEST_METHOD"] == "POST")
{
$to = $_POST['to'];
$from = $_POST['from'];
$subject = $_POST['sub'];
$body = $_POST['message'];
$SMTPMail = new SMTPClient ($SmtpServer, $SmtpPort, $SmtpUser, $SmtpPass, $from, $to, $subject, $body);
$SMTPChat = $SMTPMail->SendMail();
}
?>
<form method="post" action="">
To:<input type="text" name="to" />
From :<input type='text' name="from" />
Subject :<input type='text' name="sub" />
Message :<textarea name="message"></textarea>
<input type="submit" value=" Send " />
</form>