The IMAP4 service in MERCUR Messaging 2005 before Service Pack 4 allows remote attackers to cause a denial of service (crash) via a message with a long subject field.
https://exchange.xforce.ibmcloud.com/vulnerabilities/27229
http://www.vupen.com/english/advisories/2006/2354
http://www.securityfocus.com/bid/18462