Secunia Security Advisory – Ubuntu has issued an update for courier-mta. This fixes a vulnerability, which potentially can be exploited by malicious people to cause a DoS (Denial of Service).
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/47142/sa20548.txt
Source: https://packetstormsecurity.com/files/47142/Secunia-Security-Advisory-20548.html