Both qmail-smtpd instances can share the tcp.smtp.cdb file without
trouble. Now that you actually brought up routing...I see that I have
made a mistake. You must do your scanning with the /var/qmail instance
or which ever vpopmail does it changes on. The other qmail instance must
be the one that faces the internet. That should share the same rcpthosts
file with the vpopmail supported qmail. Then you setup smtproutes to
point all the domains to the scanning instance (/var/qmail). I have not
looked at John's patches but I suspect you might need something else for
recipient verification on the Internet facing instance...does your
vpopmail installation support mysql?
John Simpson's validrcppto will handle user verification provided you
build the cdb file with his mkvalidrcptto script for the Internet facing
qmail instance if your vpopmail does not use mysql. Also, the scanner
instance will then not need recipient verification support at all.