This section is growing too much to keep in one place.
qmailrocks.org - a qmail installation guide
Nice howto for qmail, vpopmail, courier-imap, ucspi-tcp, ezmlm, and authsmtp
Shot version of installing qmail, vpopmail, sqwebmail, qmailadmin.
How qmail processes mail.
Long version (not as accurate) of installing qmail, vpopmail, sqwebmail, qmailadmin.