PHP mailer Error receiving an email - php

Question

I am using the code below for the mailing list of the website I am working on, and it's working fine on my localhost using my credentials and on some other server using some other credentials were given to me.
<?php
if(isset($_POST['submit']))
{
require("class.phpmailer.php");
$mail = new PHPMailer();
$query = "SELECT * FROM mailing_list";
$result = mysqli_query($connect, $query)
or die('Error querying the database!');
$mail->IsSMTP();
$mail->Host= "smtp";
$mail->Username= "some email address was given to me";
$mail->Password= "password";
$mail->SMTPAuth= true;
$mail->SMTPSecure = 'tls';
$mail->From ="some email address was given to me";
$mail->FromName ="CSCA";
while($row = mysqli_fetch_array($result))
{
$first_name = $row['first_name'];
$last_name = $row['last_name'];
$to = $row['email'];
$mail->ClearAddresses();
$mail->AddAddress($to);
$mail->Subject= $_POST['subject'];
$mail->Body = "Dear $first_name $last_name,\n" . $_POST['body'];
$mail->WordWrap = 50;
if(!$mail->Send())
{
echo 'Message was not sent.';
echo 'Mailer error: ' . $mail->ErrorInfo;
}
Now when I use the following code for the contact us page of the same website it works fine one my localhost using my own credentials, but it doesn't work on the other server I used above. I got a message in the spam 'mail delivery failed'. I don't know how with the same credentials you can send mail but you can't receive! I mean with the same server and same credentials you the mailing list works fine but the contact us form gives an error. Is there a way to fix that??
Thanks in advance!
<?php
require("class.phpmailer.php");
$mail = new PHPMailer();
$name = $_REQUEST['name'];
$email = $_REQUEST['email'] ;
$message = $_REQUEST['message'] ;
$mail->IsSMTP();
$mail->Host="smtp";
$mail->Username="some email address was given to me";
$mail->Password="password";
$mail->SMTPAuth=true;
$mail->SMTPSecure = 'tls';
$mail->From =$email;
$mail->FromName =$name;
$mail->AddAddress("some email address was given to me", "Some name");
$mail->IsHTML(true);
$mail->Subject = "You have received feedback from your website!";
$mail->Body = $message;
$mail->AltBody = $message;
if(!$mail->Send())
{
echo "Message could not be sent. <p>";
echo "Mailer Error: " . $mail->ErrorInfo;
exit;
}