Dovecot in Apple Mac OS X 10.6 before 10.6.3, when Kerberos is enabled, does not properly enforce the service access control list (SACL) for sending and receiving e-mail, which allows remote authenticated users to bypass intended access restrictions via unspecified vectors.
http://support.apple.com/kb/HT4077
http://lists.apple.com/archives/security-announce/2010//Mar/msg00001.html