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[OT] Re: Sendmail forward to exchange

A simple way to do this is to have separate DNS servers serving the same
zones, one for the "outside" and one for the "inside."  When Internet
systems do an MX query for your mail domain(s), they get the address of
your Debian SMTP gateway.  Your gateway box should use the inside DNS
system for queries.  When it performs an MX lookup for the the same mail
domain(s) (which sendmail in the process of trying to deliver the mail),
it'll get the address of the Exchange system and relay on to it.  As far
as I know, this is a fairly common configuration; it's how I've done it in
the past.  There is dicussion of this internal/external DNS strategy in
"Building Internet Firewalls"  (Chapman and Zwicky), and probably in other
places as well.  Take care to configure sendmail to relay only the domains
for which you have an MX record, otherwise you'll be setting up an open

Hope that helps,

On Tue, 14 May 2002, Marcel Welschbillig wrote:

> Can anyone tell me how to setup sendmail to forward all INCOMING mail to
> an exchange server ? I have a Debian firewall running send mail with an
> exchange server behind the fire wall on a private IP. I would like all
> mail to be MXed to the Debian box and then forwarded to the Exchange box.

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