> You can use Postfix's probing (or Exim's callout) to query the Exchange 'server' provided it is set up to reject invalid recipients. As pointed out if this is not done Exchange will happily take any old rubbish and bounce it some time later. Alternatively have the MTA make an LDAP callout to AD. Exchange is basically an AD schema extension so it's reasonably easy to do - but network chatter is a PITA.
To solve that annoying Exchange 'I take any mail dot com...' issue: To enable valid recipients only.... >1) Expand ESM, Message Delivery. >2) Right click on "Message Delivery" and choose Properties. >3) Click on the tab "Recipient Filtering". >4) Enable the option "Filter Recipients who are not in the directory." You then need to enable the Recipient Filter on the SMTP Server. >1) Still in ESM, Expand Admin Groups, , Server, , Protocols, SMTP. This is assuming he's on 2003 or earlier, if you're on 07 or higher it will be enabled by default ONLY if edge servers are being used, otherwise it has to be enables through the shell (Exchange management shell)
