require 'phpmailer/PHPMailerAutoload.php';

if(isset($_POST['submit'])) {
$mail = new PHPMailer;
$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];
$email = $_POST['email'];
$subject = $_POST['subject'];
$message = $_POST['message'];

$mail->isSMTP();
$mail->Host = 'mailout.one.com';
$mail->SMTPAuth = true;
$mail->Username = 'myemail@one.com';
$mail->Password = 'mypassword';
$mail->SMTPSecure = 'tls';
$mail->Port = 465;
$mail->AddReplyTo($email, $firstName);
$mail->setFrom($email, $firstName);
$mail->addAddress('example@gmail.com', 'the name');
$mail->isHTML(true);
$mail->Subject = $_POST['subject'];
$mail->Body    = '<b>From:</b><br> ' . $firstName . ' ' . $lastName . '<br> <br> <b>Message:</b> <br> ' .$message;
$mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

$mail->SMTPDebug = 3;

$mail =  new PHPMailer;
$mail->Host = 'mailout.one.com';
$mail->SMTPAuth = true;
$mail->Username = '***************';
$mail->Password = '************';
$mail->SMTPSecure = false;
$mail->Port = 25;

/*be careful with the one.com servers strict case sensitivity
renaming the file PHPMailerAutoload.php to phpmailerautoload.php could do the trick, but you need to require it in lower case as well:*/
require_once 'phpmailer/phpmailerautoload.php';

$mail = new PHPMailer;  //don't use brackets here!
$mail->IsSMTP();
$mail->SMTPAuth = true;
$mail->SMTPSecure = "tls";
$mail->Host = "send.one.com";
$mail->Port = 587;
$mail->Username = "**toChangeTp**your webemail-username";
$mail->Password = "**toChangeTp**your webmail-passwort";

$useExceptions = true;
$mail = new PHPMailer( $useExceptions );
try {
   $mail->isSMTP();
   $mail->Host = 'send.one.com';
   $mail->SMTPAuth = true;
   $mail->Username = 'xxx@yyy.zz';  // Replace by your SMTP username
   $mail->Password = 'xxx123489';   // Replace by your SMTP password
   $mail->SMTPSecure = 'tls';
   $mail->Port = 587;
   ...
   $mail->setFrom('Your email-fromaddress>');  // Replace
   $mail->addAddress('Your to address');       // Replace
   $mail->addReplyTo('Your Reply Address');    // Replace
   ...
   $mail->isHTML(true);
   $mail->Subject = 'Your Subject';
   $mail->Body    = 'Your body';
   $mail->AltBody = 'Your plain text body';
   ...
   $mail->send();
} catch (Exception $e) {
   ...
}