How-to verify valid internal email addresses --- up front

[W S]

Folks,
  I have this Hub, up in front, which process all incoming emails (running Postfix and MailScanner). This Hub is bluntly accepting ALL emails from outside and runs every single email thru MailScanner (ClamAV, Spamassassin, RBL, DNSBL etc) and relaying all JUNK to another internal email server.
  Now, is there any way to build some sort of MAP or database file (btree, hash
) from valid internal email addresses and set it on the Hub in order to reduce the queue?
  Regards,
  --W.S.

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