Common Configuration Changes

A default sendmail.cf file will be installed in /etc. The default configuration should work for most SMTP-only sites. It will not work for UUCP (UNIX to UNIX Copy) sites; you will need to generate a new sendmail.cf if you must use UUCP mail transfers.

	Note
	Although SMTP servers are supported automatically, IMAP (Internet Message Access Protocol) servers are not. If your ISP uses an IMAP server rather than an SMTP sever, you must install the IMAP package. Without it, your system won't know how to pass information to the IMAP server or retrieve your mail.

If you need to generate a new /etc/sendmail.cf file to configure Sendmail, you should utilize the m4 macro processor. If you ever edit the /etc/mail/sendmail.mc to add functionality to Sendmail, backup your current /etc/sendmail.cf file, generate a new one by executing the m4 /etc/mail/sendmail.mc > /etc/sendmail.cf command, and add any previous changes from the /etc/sendmail.cf you backed up to the new /etc/sendmail.cf file. After creating a new /etc/sendmail.cf, you must restart Sendmail to make it take effect. The easiest way to do this is to type the /sbin/service sendmail restart command as root.

By default, the m4 macro processor is installed with Sendmail. The m4 macro processor is included with the sendmail-cf package, which is installed in /usr/lib/sendmail-cf.

You should consult the /usr/lib/sendmail-cf/README file before you edit any of the files in the directories under the /usr/lib/sendmail-cf directory, as they can affect how future /etc/sendmail.cf files are configured.

	Warning!
	Do not use Linuxconf to configure Sendmail! The Linuxconf module mailconf, designed to make editing /etc/sendmail.cf easier, is broken and contains out-of-date information about rule sets used in Sendmail configuration.

One common Sendmail configuration is to have a single machine act as a mail gateway for all the machines on your network. For instance, a company may want to have a machine called mail.bigcorp.com that does all our mail. On that machine, we simply need to add the names of machines for which mail.bigcorp.com will handle mail to /etc/mail/local-host-names. Here is an example:

# sendmail.cw - include all aliases for your machine
# here.
torgo.bigcorp.com
poodle.bigcorp.com
devel.bigcorp.com

Then on the other machines, torgo, poodle, and devel, we need to edit /etc/sendmail.cf to "masquerade" as mail.bigcorp.com when sending mail and to forward any local mail processing to bigcorp.com. Find the DH and DM lines in /etc/sendmail.cf and edit them as such:

# who I send unqualified names to
# (null means deliver locally)
DRmail.bigcorp.com
      
# who gets all local email traffic 
DHmail.bigcorp.com
      
# who I masquerade as (null for no masquerading)
DMbigcorp.com

With this type of configuration, all mail sent will appear as if it were sent from bigcorp.com, and any mail sent to torgo.bigcorp.com or the other hosts will be delivered to mail.bigcorp.com.

Please be aware that if you configure your system to masquerade as another, any email 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@poodle.bigcorp.com> by the cron daemon would be sent to <root@mail.bigcorp.com>.