Yes, unless you've specificially configured Exchange to forward unknown recipients to another mail host. You would typically do this when sharing SMTP namespace with foreign mail systems.
How to share an SMTP address space in Exchange 2000 Server or in Exchange Server 2003
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From: exchangelist-bounce@xxxxxxxxxxxxx [exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Douglas Long [admindoug@xxxxxxxxx]
Sent: Thursday, September 16, 2010 12:26 PM
Subject: [ExchangeList] Exchange 2003 contact routing handled differently
I am not sure if I missed something long ago, or this is acting weird. If I have a domain catdog.com that my Exchange org is serving, shouldn't all messages sent to @catdog.org from internal MAPI clients stay within Exchange?
What is happening (Exchange 2003) ....
I have a contact jdaily with smtp address of jdaily@xxxxxxxxxx. Of course there is no Exchange mailbox for this address or it wouldn't be a contact. I would figure messages to this address would just be bounced, but instead are forwarded onto a UNIX host which forwards messages to various addresses (like a dist group).
Can anyone explain this? I am at a loss.