Chip Salzenberg Deliver does not properly associate a lockfile with the user who created the file, which allows local users to cause a denial of service (blockage of incoming e-mail) by creating lockfiles for arbitrary mailboxes.
https://exchange.xforce.ibmcloud.com/vulnerabilities/57558
http://www.securityfocus.com/bid/38924
http://www.securityfocus.com/archive/1/510306/100/0/threaded