PHP: Mail headers

mail_headers.php

<?php

$headers = [
	'MIME-Version: 1.0',
	'Content-Type: text/html; charset="UTF-8";',
	'Content-Transfer-Encoding: 7bit',
	'Content-Disposition: inline',
	'Date: ' . date('r', $_SERVER['REQUEST_TIME']),
	'Message-ID: <' . $_SERVER['REQUEST_TIME'] . md5($_SERVER['REQUEST_TIME']) . '@' . $_SERVER['SERVER_NAME'] . '>',
	'From: ' . $from,
	'Reply-To: ' . $from,
	'Return-Path: ' . $from,
	'X-Mailer: PHP v' . phpversion(),
	'X-Originating-IP: ' . $_SERVER['SERVER_ADDR'],
	'X-Priority: 1 (Higuest)',
	'X-MSMail-Priority: High',
	'Importance: High',
	'Sensitivity: Personal',
];


// Sensitivity: Normal, Personal, Private and Company-Confidential
// These will be recognised and handled in Outlook, Thunderbird and others.