QMail RCPT Denial of Service Vulnerability
Setting user resource limits on the server process will prevent Qmail from allocating enough memory to cause a denial of service.
The following command will set the maximum amount of memory processes can allocate in the heap to 1 MB.
'ulimit -d 1024'.
If placed in the init scripts, the limit will be put in place whenever the system intializes.
This information was supplied by Dan Bernstein <firstname.lastname@example.org>.