Exim before 4.87.1 might allow remote attackers to obtain the private DKIM signing key via vectors related to log files and bounce messages.
https://bugs.exim.org/show_bug.cgi?id=1996
http://www.ubuntu.com/usn/USN-3164-1
http://www.securitytracker.com/id/1037484
http://www.securityfocus.com/bid/94947