IIS SMTP gateway

For a number of reasons I'm looking at setting up a IIS box as an SMTP relay before the mail server. Like the setup below:

mail server

An important point to note is that this SMTP relay must be able to relay in both directions. That is all email that travels between the internet and the mailserver must travel though the gateway.

I am pretty certain that this can be done, but I'm having some difficulties conceptualising how it is done. I can understand how the IIS server could be configured to relay all mail going in one direction, but not both. Talking through it (as I understand it):
Inbound - easy. relay all mail to the mail server by setting the smart host to the mail server for the default domain.
Outbound - easy. Set the mail server to relay to the IIS box (set IIS to allow relay from the mailserver's IP addr) and let the IIS box handle delivery.
Both: As I see it setting one stops the other from working.

A number of articles have pointed to this as a possibility, however none have gone through the process of setting up the box.

The mail server in question could be any one of a number of mail servers, so please, no suggestions that involve running something on the Exchange/Groupwise/Lotus server. This has to be able to run on a standalone box.

David Cameron
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David WilhoitSenior Consultant, ExchangeCommented:

You've probably seen this, but thought I'd lay it out here anyhow...another is this:

Configure the other servers to use your relay server as a smart host
Depending on the other applications or mailers that will use your relay server, you may have a option where you can specify a smart host or SMTP relay. With Exchange 2000, you would create an SMTP connector and specify the Windows 2000 Relay server in the Forward all mail through this connector to the following smart host box.

That's pretty much it. I'd configure spam filtering on my SMTP box as well, takes the load off the mail server, and reduces the security risks.


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David_CameronAuthor Commented:
Thanks very much for the help.

Let me see if I have this clear. I create a domain (eg davidcameron.com) which is the domain for the mail server. In that domain I set the smart host to the mail server. Then in Exchange I set it to relay all mail to the IIS box. So emails hitting the IIS box sent to *@davidcameron.com allways go to the mail server, all other emails go to wherever IIS can deliver them.

David Cameron
David WilhoitSenior Consultant, ExchangeCommented:
SMTP VS: Create new domain, remote. Give it a domain name, such as davidcameron.com. Allow mail for this domain to be relayed, forward to smart host, [xx.xx.xx.xx] format.

Exchange 2000/2003: Create SMTP connector. Configure the bridgehead server, use the default SMTP VS located on the Exchange server, forward all outbound mail to the Windows 2000/2003 SMTP server, as configured above. It's actually very straight-up..
David_CameronAuthor Commented:
Many thanks for the help.

You are right, it is simple once you know how.

David Cameron
David WilhoitSenior Consultant, ExchangeCommented:
you're very welcome!

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