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Comments and suggestions concerning this book should be mailed to gmourani@videotron.ca © Copyright 1999-2000 Gerhard Mourani and Open Network Architecture ® 262 dnl file. If you modify this file you will have to regenerate the dnl /etc/sendmail.cf by running this macro config through the m4 dnl preprocessor: dnl dnl        cp sendmail.8.9.3.tar.gz /var/tmp dnl        cd /var/tmp dnl        tar xzpf sendmail.8.9.3.tar.gz dnl        cd /var/tmp/sendmail-8.9.3/cf/cf dnl        m4 ../m4/cf.m4 /etc/null.mc > /etc/sendmail.cf dnl dnl You will need to have the sendmail source distribution for this to  dnl work. divert(0) OSTYPE(`linux') FEATURE(`nullclient',`mail.openarch.com') undefine(`ALIAS_FILE') This tells null.mc file to set itself up for this particular configuration setup with: divert(-1) and divert(0) The divert(-1) will delete the crud in the resulting output file and the divert(0) restores regular output. OSTYPE(`linux’) This configuration option specifies the default operating system Sendmail will running on, in our case the “linux” system. This item is one of the minimal information requiring by the “mc” file. FEATURE(`nullclient',`mail.openarch.com') This m4 macro set your clients machines to never receive mail directly, send their mail to a Central Mail Hub and they relay all mail through that server rather than sending directly. This feature creates a stripped down configuration file containing nothing but support for forwarding all mail to a Mail Hub via a local SMTP-based network. The argument `mail.openarch.com’ included in this feature is the canonical name of that Mail Hub. You should, of course, change this canonical name to reflect your Mail Hub Server for  example: FEATURE(`nullclient',` my.mailhub.com'). undefine(`ALIAS_FILE') This configuration option prevent the nullclient version of Sendmail from trying to access “/etc/aliases” and “/etc/aliases.db” files. With the adding of this line in the “.mc” file, you don’t need to have “aliases” file on all your internal neighbor client Sendmail machines. Aliases file is require only on the Mail Hub Server for all server and client aliases on the network. Now that our macro configuration file “null.mc” is create, we can build the Sendmail configuration file “sendmail.cf” from these statements in all our neighbor server, client machines with the following commands: [root@deep /]# cd /var/tmp/sendmail-version/cf/cf/ [root@deep cf]# m4 ../m4/cf.m4 /etc/null.mc > /etc/sendmail.cf Step 2 No mail should ever again be delivered to your local machine. Since there will be no incoming mail connections, you no longer needed to run a Sendmail daemon on your neighbor or local server, client machines.