Only allow external routing via SMTP from inside network

Hello,

We have an Exchange server 2003 in our Company.
We already now how to allow external routing in our exchange server(Connector Properties - Allow Messages to be relayed to these domains)

the problem is, people from outside our network, can also use this function. What we want is, inside our company, internal network, it should be possible to send emails through smtp to people outside our domain, but when on the outside, the smtp should only be able to send emails to our employees.

Is that possible to do?
Or should i solve this some other way?

The reason we want this is for our support website to be able to send automatic status updates to the customers from an ASP.NET website.
LVL 4
Joachim CarreinSr. Software DeveloperAsked:
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InteraXConnect With a Mentor Commented:
Hi joachimcarrein,

It sounds like you want to allow your application to relay SMTP traffic through your exchange system. Is that correct?

See http://www.microsoft.com/technet/security/prodtech/exchangeserver/excrelay.mspx#EXC

Good Luck,

Chris
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SembeeCommented:
Exchange does what you have described by default.
The option you have described is on the SMTP Connector and if it is enabled on an SMTP Connector with the * as the domain then you have turned the server in to an open relay.

Relaying is controlled in Exchange in one of two ways - by IP address and by authentication. The preference from a security point of view is authentication. However if your web site is internal then you could allow relaying from that machine only.

Simon.
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InteraXCommented:
Thanks. ;-)

Chris.
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