mail() is Incorrectly Sending Emails to cPanel Default Account - php

Question

I purchased a domain from GoDaddy and linked it to Office 365 (via MX records). This means I have several email accounts in Outlook that are #mydomain.com.
Example Outlook accounts:
sales#mydomain.com
contact#mydomain.com
matt#mydomain.com
I can send/receive emails through those accounts.
My website is hosted on basic web hosting with a cPanel installation, which means I was given a "default" email account. For example: default#mydomain.com. I wrote a PHP script on my website (contact form) that sends emails via mail() to contact#mydomain.com.
However all the emails are sent to the default cPanel account default#mydomain.com instead of the Outlook account contact#mydomain.com.
To test, I tried sending the emails to my personal account that is not hosted on mydomain and it works as expected. Emails are sent instantly.
How come my website incorrectly send emails to the Outlook accounts? Thanks for your time.
EDIT:
The script was requested:
<?php
$uploadedFile = $statusMsg = '';
if (isset($_POST['submit']))
{
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];
$email = $_POST['email'];
$phone = $_POST['phone'];
$message = $_POST['message'];
if(!empty($first_name) && !empty($last_name) && !empty($message))
{
if(filter_var($email, FILTER_VALIDATE_EMAIL))
{
$uploadStatus = 1;
if(!empty($_FILES["attach"]["name"]))
{
$targetDir = "uploads/";
$fileName = basename($_FILES["attach"]["name"]);
$targetFilePath = $targetDir . $fileName;
$fileType = pathinfo($targetFilePath,PATHINFO_EXTENSION);
if(move_uploaded_file($_FILES["attach"]["tmp_name"], $targetFilePath))
{
$uploadedFile = $targetFilePath;
}
else
{
$uploadStatus = 0;
$statusMsg = "Sorry, there was an error uploading your file.";
}
}
if($uploadStatus == 1)
{
$name = $first_name.' '.$last_name;
$mailTo = "contact#mydomain.com";//changed to my real outlook account
$htmlContent = '<h2>Contact Request Submitted</h2>
<p><b>Name:</b> '.$name.'</p>
<p><b>Email:</b> '.$email.'</p>
<p><b>Phone:</b> '.$phone.'</p>
<p><b>Message:</b><br/>'.$message.'</p>';
// Header for sender info
$headers = "From: $name"." <".$email.">";
if(!empty($uploadedFile) && file_exists($uploadedFile))
{
// Boundary
$semi_rand = md5(time());
$mime_boundary = "==Multipart_Boundary_x{$semi_rand}x";
// Headers for attachment
$headers .= "\nMIME-Version: 1.0\n" . "Content-Type: multipart/mixed;\n" . " boundary=\"{$mime_boundary}\"";
// Multipart boundary
$message = "--{$mime_boundary}\n" . "Content-Type: text/html; charset=\"UTF-8\"\n" .
"Content-Transfer-Encoding: 7bit\n\n" . $htmlContent . "\n\n";
// Preparing attachment
if(is_file($uploadedFile)){
$message .= "--{$mime_boundary}\n";
$fp = #fopen($uploadedFile,"rb");
$data = #fread($fp,filesize($uploadedFile));
#fclose($fp);
$data = chunk_split(base64_encode($data));
$message .= "Content-Type: application/octet-stream; name=\"".basename($uploadedFile)."\"\n" .
"Content-Description: ".basename($uploadedFile)."\n" .
"Content-Disposition: attachment;\n" . " filename=\"".basename($uploadedFile)."\"; size=".filesize($uploadedFile).";\n" .
"Content-Transfer-Encoding: base64\n\n" . $data . "\n\n";
}
$message .= "--{$mime_boundary}--";
$returnpath = "-f" . $email;
// Send email
$mail = mail($mailTo, "Contact Form Submission from ".$name, $message, $headers, $returnpath);
// Delete attachment file from the server
#unlink($uploadedFile);
}
else
{
// Set content-type header for sending HTML email
$headers .= "\r\n". "MIME-Version: 1.0";
$headers .= "\r\n". "Content-type:text/html;charset=UTF-8";
// Send email
$mail = mail($mailTo, 'Contact Form Submission from '.$name, $htmlContent, $headers);
}
// If mail sent
if($mail)
{
$statusMsg = "Your message has been sent. Thanks!";
}
else
{
$statusMsg = 'Your contact request submission failed, please try again.';
}
}
}
else
{
$statusMsg = 'Please enter a valid email address.';
}
}
else
{
$statusMsg = "Please fill out the required information.";
}
}
?>

Answer 1

The solution was to change my cPanel "Email Routing" option to "Remote" in order for all local emails to first check with the MX records.