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Mail Server Question

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by rangers fan

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I'm pretty new to email servers, but have sort of an odd question. My company has an exchange server and the "powers that be" want to put it on the net as an SMTP server. Knowing Exchange's track record involving security holes and virii and spam,along with the stability and security of NT, is there a way to say setup a qmail or sendmail server (running Linux, or *BSD) for the internet mail and relay all of the messages to the exchange box and vice versa for outgoing mail? I don't have a speedy machine left for this, so I was thinking about qmail for the server (since everything I have read about claim that it is speedy) but couldn't find a FAQ on how to relay a message between servers (the exchange part I'm not too worried about), butfor the qmail/sendmail server, I have set it up just listening to localhost and as a POP server (internal), but not sure about the routing of email between servers.

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by stillatit

1. Block access to the Exchange box from the Internet using your firewall.
2. Have your unix/linux box visible to the internet.
3. Set the MX records in DNS so that your Exchange box is the preferred mail server and the unix/linux box is the secondary mail server. Outside sites will try to send mail to the Exchange box, fail to connect, then send to the unix/linux box. Once the unix/linux box has a piece of mail, it notes that there is a preferred server for the domain, and forwards the mail to the Exchange box, which it CAN reach. Note that this introduces some delay. Note also that you must carefully set up the unix/linux box to foward to the Exchange server only mail for your domain, and to refuse to relay anything else.
4. On the outgoing side, set the Exchange server to use a mail gateway for outgoing mail, and designate either the unix/linux server or your ISP's mail server if they so allow. (The control is called "Forward all messages to Host" on the Internet Mail Service "Connections" tab.)

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