SMTP Routing Based On Recipient

[Adam Ellis <aellis@saberlogic.com>]

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I am running a MS Exchange 5.5 server and am getting hit with the NDR
(non-delivery report) Reverse Spam Attack as described here:
 
http://www.tek-tips.com/gviewthread.cfm/lev2/3/lev3/15/pid/10/qid/725829

As the thread describes, there is no way to just turn off NDRs in
Exchange 5.5 - Microsoft is recommending third party utilities.  What I
am wondering is this - would it be possible to redirect SMTP to my Linux
server, use iptables to check that the recipient matches a valid user
from a list I'd supply, and, if so, route the message to the Exchange
server?  And, if no valid recipient is found, the message is simply
dropped.  Is this even a logical way to handle this situation?  Should I
be looking at something like snort instead?  I'm all ears!

Thanks,
-- 
Adam Ellis <aellis@saberlogic.com>
SaberLogic

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