source: https://www.securityfocus.com/bid/23145/info PHP is prone to an email-header-injection vulnerability because it fails to properly sanitize user-supplied input when constructing email messages. Exploiting this issue allows a malicious user to create arbitrary email headers, and then create and transmit spam messages from the affected computer. The following versions are vulnerable: PHP 4 up to and including 4.4.6 PHP 5 up to and including 5.2.1 <?php mail("test@domain(dot)com", "Test\r\n \nAnother-Header: Blub", "Message"); ?>