Enigmail 1.7.x before 1.7.2 sends emails in plaintext when encryption is enabled and only BCC recipients are specified, which allows remote attackers to obtain sensitive information by sniffing the network.
https://security.gentoo.org/glsa/201504-01
https://advisories.mageia.org/MGASA-2014-0421.html
http://www.openwall.com/lists/oss-security/2014/08/22/1
http://sourceforge.net/p/enigmail/forum/support/thread/3e7268a4/
http://sourceforge.net/p/enigmail/bugs/294/
http://secunia.com/advisories/61854
http://secunia.com/advisories/60887
http://secunia.com/advisories/60779
http://lists.opensuse.org/opensuse-updates/2014-09/msg00008.html
http://lists.opensuse.org/opensuse-updates/2014-09/msg00004.html