The IMAP functionality in Dovecot before 2.2.2 allows remote attackers to cause a denial of service (infinite loop and CPU consumption) via invalid APPEND parameters.
http://www.securitytracker.com/id/1028585
http://www.openwall.com/lists/oss-security/2013/05/24/1
http://www.dovecot.org/list/dovecot-news/2013-May/000255.html