OpenSMTPD before 5.3.2 does not properly handle SSL sessions, which allows remote attackers to cause a denial of service (connection blocking) by keeping a connection open.
https://exchange.xforce.ibmcloud.com/vulnerabilities/84388
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-2093
http://secunia.com/advisories/53353
http://seclists.org/oss-sec/2013/q2/366
http://seclists.org/oss-sec/2013/q2/362
http://git.zx2c4.com/OpenSMTPD/commit/?id=38b26921bad5fe24ad747bf9d591330d683728b0