Unknown vulnerability in the SMTP server in Lotus Domino 5.0 through 5.7 allows remote attackers to bypass mail relaying restrictions via crafted e-mail addresses in "RCPT TO" commands.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6591
http://www.kb.cert.org/vuls/id/176972
http://www-1.ibm.com/support/docview.wss?rs=899&uid=swg21085603