The /etc/mail/local-host-names file

Securing and Optimizing Linux: RedHat Edition -A Hands on Guide
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# 22.8. The `/etc/mail/local-host-names` file

> : Please note that the `/etc/mail/local-host-names` file is for all type of configuration.

The `/etc/mail/local-host-names` file is read to obtain alternative names for the local host. One use for such a file might be to declare a list of hosts in your network for which the local host is acting as the `MX` recipient. On that machine we simply need to add the names of machines for which it i.e. `mail.openna.com`, will handle mail to `/etc/mail/local-host-names`. Here is an example:

Example 22-2. Alternative names

Create the local-host-names file, touch `/etc/mail/local-host-names` and add the following line:

             # local-host-names - include all aliases for your machine here.
             openna.com
             deep.openna.com
             www.openna.com
             win.openna.com
             mail.openna.com

With this type of configuration, all mail sent will appear as if it were sent from `openna.com`, and any mail sent to `www.openna.com` or the other hosts will be delivered to `mail.openna.com` our mail Hub.

Please be aware that if you configure your system to masquerade as another, any e-mail sent from your system to your system will be sent to the machine you are masquerading as. For example, in the above illustration, log files that are periodically sent to `<root@www.openna.com>` by the cron daemon of Linux would be sent to `<root@mail.openna.com>` our Mail Hub.

## 22.8.1. Configure the `/etc/sysconfig/sendmail` file

The `/etc/sysconfig/sendmail` file is used to specify `SENDMAIL` configuration information, such as if sendmail should run as a daemon, if it should listen for mail or not, and how much time to wait before sending a warning if messages in the queue directory have not been delivered.

Create the sendmail file touch `/etc/sysconfig/sendmail` and add in this file:

             DAEMON=yes
             QUEUE=1h

  The `DAEMON=yes` option instructs Sendmail to run as a daemon. This line is useful when Sendmail client machines are configured to not accept mail directly from outside in favor of forwarding all local mail to a Central Hub, not running a daemon also improves security. If you have configured your server or client machines in this way, all you have to do is to replace the `DAEMON=yes` to `DAEMON=no`.
  Mail is usually placed into the queue because it could not be transmitted immediately. The `QUEUE=1h` sets the time interval before sends a warning to the sender if the messages has not been delivered.

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