Im getting the delivery failed from the post master reply. i don't want it.
because then poeple can find out all my real users on the exchange.
also, i have a lot of users (10K) in my application – and i don't want to create a mailbox for each user.
is it possible to get this done in ex2010 sp1. hub-transport configuration?
or i must use edge-transport as indicated in http://technet.microsoft.com/en-us/library/bb691132(EXCHG.80).aspx
Best Answer
The NDRs generated by non-existent email addresses are very important. How else would a sender know they have made a mistake and addressed an email incorrectly?
Here is an article about why NOT to use catch all addresses: http://www.allspammedup.com/2010/05/why-you-should-not-use-a-catch-all-email-address/
If you're worried about directory harvesting attacks (where attackers send lots of email to your network and use the NDRs to determine valid and invalid addresses) then you can combat that with any email security product that includes directory harvesting protection.
GFI products do this.
Or you can do it with Exchange 2010's inbuilt security features, by configuring the tarpit interval. Read this article (scroll down to the part about tarpitting):
http://technet.microsoft.com/en-us/library/bb123891.aspx
You can read more about directory harvesting here too (refers to Exchange 2007 but applies to Exchange 2010 as well): http://www.allspammedup.com/2008/12/protecting-exchange-server-2007-from-directory-harvesting-attacks/