Sendmail

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

	Please 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.

To generate a new sendmail.cf, you will need to install m4 and the sendmail source package. Read the README file in the sendmail sources for more details on creating sendmail configuration files. Also, O'Reilly & Associates publishes a good sendmail reference entitled sendmail, by Bryan Costales.

One common sendmail configuration is to have a single machine act as a mail gateway for all the machines on your network. For instance, at Red Hat we have a machine mail.redhat.com that does all our mail. On that machine we simply need to add the names of machines for which mail.redhat.com will handle mail to /etc/sendmail.cw. Here is an example:

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

Then on the other machines, torgo, poodle, and devel, we need to edit /etc/sendmail.cf to "masquerade" as mail.redhat.com when sending mail, and to forward any local mail processing to redhat.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.redhat.com
# who gets all local email traffic 
DHmail.redhat.com
# who I masquerade as (null for no masquerading)
DMredhat.com

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

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@poodle.redhat.com> by the cron daemon would be sent to <root@mail.redhat.com>.