Sendmail 8.9.0 through 8.12.6 allows remote attackers to bypass relaying restrictions enforced by the 'check_relay' function by spoofing a blank DNS hostname.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A8512
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A6892
https://exchange.xforce.ibmcloud.com/vulnerabilities/10775
http://www.vupen.com/english/advisories/2009/3539
http://www.sendmail.org/8.12.7.html
http://www.securityfocus.com/bid/6548