Webmail in MailEnable Professional Edition before 1.73 and Enterprise Edition before 1.21 allows remote attackers to cause a denial of service (CPU consumption) via unspecified vectors involving "incorrectly encoded quoted-printable emails".
https://exchange.xforce.ibmcloud.com/vulnerabilities/25315
http://www.vupen.com/english/advisories/2006/1006
http://www.securityfocus.com/bid/17161
http://www.mailenable.com/professionalhistory.asp