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has anyone hacked QMail or Sendmail so that it could act as a mail server
without actually having accounts on it?

The idea that I have is that when a user gets mail (ala SMTP connection
coming in), or the user checks mail (ala POP connection coming in), the
mail server (Qmail, Sendmail, whatever) could make an ODBC/SQL call to a
NT Server running MS-SQL (doesn't really matter, as it is a pure ODBC
call). Has anyone done anything like this? Just curious. Thanks in
advance. Pointers would be good also.