Using Mailscanner on FreeBSD to deliver mail to an Exchange Server

MailScanner is an excellent spam filter from Julian Field at the University of Southampton It will run on any version of Unix but I've found FreeBSD very easy to set up. These pages will try and document the process I used.

The basic idea is that you publish an MX record in your public DNS which points to the MailScanner box. This means that mail gets delivered to this. MailScanner then scans the mail and passes it on for delivery. When it does this it looks up the MX record for your domain but this time from an internal DNS server which will point to your internal Exchange server. Exchange gets the email and then delivers it to the user