In this section we will look how you can start off with an initial mc file, and how to compile your own .cf file to a cf file. There are many interesting example mc files available in /usr/share/sendmail/cf/cf. The most interesting examples are sendmail-slackware.mc (which is used for generating the default Slackware Linux sendmail.cf), and sendmail-slackware-tls.mc which adds TLS support to the standard Slackware Linux sendmail configuration. If you want to create your own sendmail configuration, it is a good idea to start with a copy of the standard Slackware Linux mc file. For instance, suppose that we would like to create a configuration file for the server named straw, we could execute:

# cd /usr/share/sendmail/cf/cf
# cp sendmail-slackware.mc sendmail-straw.mc
      

and start editing sendmail-straw.mc. After the configuration file is modified to our tastes, M4 can be used to compile a cf file:

# m4 sendmail-straw.mc > sendmail-straw.cf
      

If we want to use this new configuration file as the default configuration, we can copy it to /etc/mail/sendmail.cf:

# cp sendmail-straw.cf /etc/mail/sendmail.cf
      

If you would like to use another host to deliver e-mail to locations to which the sendmail server you are configuring can not deliver you can set up sendmail to use a so-called “smart host”. Sendmail will send the undeliverable e-mail to the smart host, which is in turn supposed to handle the e-mail. You do this by defining SMART_HOST in your mc file. For example, if you want to use smtp2.example.org as the smart host, you can add the following line:

define(`SMART_HOST',`stmp2.example.org')
      

By default sendmail will accept mail destined for localhost, and the current hostname of the system. You can simply add additional hosts or domains to accept e-mail for. The first step is to make sure that the following line is added to your mc configuration:

FEATURE(`use_cw_file')dnl
      

When this option is enabled you can add host names and domain names to accept mail for to /etc/mail/local-host-names. This file is a newline separated database of names. For example, the file could look like this:

example.org
mail.example.org
www.example.org
      

Often you may want to map e-mail addresses to user names. This is needed when the user name differs from the part before the “@” part of an e-mail address. To enable this functionality, make sure the following line is added to your mc file:

FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl
      

The mappings will now be read from /etc/mail/virtusertable.db. This is a binary database file that should not directly edit. You can edit /etc/mail/virtusertable instead, and generate /etc/mail/virtusertable.db from that file.

The /etc/mail/virtusertable file is a simple plain text file. That has a mapping on each line, with an e-mail address and a user name separated by a tab. For example:

john.doe@example.org    john
john.doe@mail.example.org        john
      

In this example both e-mail for john.doe@example.org and john.doe@mail.example.org will be delivered to the john account. It is also possible to deliver some e-mail destined for a domain that is hosted on the server to another e-mail address, by specifying the e-mail address to deliver the e-mail to in the second in the second column. For example:

john.doe@example.org    john.doe@example.com
      

After making the necessary changes to the virtusertable file you can generate the database with the following command:

# makemap hash /etc/mail/virtusertable < /etc/mail/virtusertable