There's been progress in officially including the packages into the Debian archive since. As of Sun, 29 Jun 2008, the following packages are officially available for Debian/sid and Debian/lenny:
There's been a netqmail-1.06 package (binary packages qmail, qmail-uids-gids), a qmail-run package, and a qmail-tools package, which should be extended to enable upgrades from previous versions of qmail binary packages, uploaded to Debian on Mon, Apr 28, 2008.
New packages usually are included into the official Debian archive after review by the ftpmasters within one or two weeks, the reasons why this does not happen with the qmail packages I don't know. Asking unfortunately doesn't help, there's no reply.
Update: On Sun, 06 Jul 2008, I received this email.
deb http://dbn.smarden.org/ sid/ deb-src http://dbn.smarden.org/ sid/to /etc/apt/sources.list, and run
# apt-get updateThen install the packages as usual with apt-get, dpkg or dselect.
There is a mailing list you should join when installing these packages. To subscribe send an empty email to <debian-packages-subscribe@list.smarden.org>. The mailing list will most probably be closed, once the packages are available officially through the Debian archive.