CipherTrust IronMail 5.0.1, when "Denial of Service Protection" is enabled, allows remote attackers to cause a denial of service (possibly CPU consumption) via a SYN flood with malformed TCP packets from multiple connections.
https://exchange.xforce.ibmcloud.com/vulnerabilities/24445
http://www.securityfocus.com/bid/16465
http://www.securityfocus.com/archive/1/423898/100/0/threaded