Installing Erwin Hoffmann's SMTP AUTH patch to qmail-smtpd:

Change into your qmail/netqmail source directory.
Untar the qmail-smtpd-auth archive.
call `./install_auth.sh`
run `make`
run `make setup`

Latest version can be found at:  http://www.fehcom.de/qmail/smtpauth.html
