Quoting from the home page of qmail, where you can find more information as well as the package itself:
qmail is a secure, reliable, efficient, simple message transfer agent. It is meant as a replacement for the entire sendmail-binmail system on typical Internet-connected UNIX hosts.
Below, you will find some scripts and small programs that have helped me to run qmail efficiently. Use them if you wish, but beware: Though I try to write carefully, I can not quarantee that this is either bug free or secure. Caveat emptor and all that.