Mac OS X Server v10.5, 10.6: Preventing your mail server from being spoofed

Mac OS X Server v10.5 and later utilizes ClamAV and SpamAssassin to check for spam and potential viruses as incoming mail is processed. By adding a few lines into /etc/postfix/main.cf, you can utilize Postfix to assist in filtering messages that are being received from servers masquerading as your mail server.