Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual page 409

/sbin/service sendmail restart
Important
The default sendmail.cf file does not allow Sendmail to accept network connections
from any host other than the local computer. To configure Sendmail as a server for
other clients, edit the /etc/mail/sendmail.mc file, and either change the address
specified in the Addr= option of the DAEMON_OPTIONS directive from 127.0.0.1 to the
IP address of an active network device or comment out the DAEMON_OPTIONS directive
all together by placing dnl at the beginning of the line. When finished, regenerate /etc/
mail/sendmail.cf by executing the following command:
m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
The default configuration which ships with Red Hat Enterprise Linux works for most SMTP-only sites.
However, it does not work for UUCP (UNIX to UNIX Copy) sites. If using UUCP mail transfers, the /
etc/mail/sendmail.mc file must be reconfigured and a new /etc/mail/sendmail.cf must be
generated.
Consult the /usr/share/sendmail-cf/README file before editing any files in the directories under
the /usr/share/sendmail-cf directory, as they can affect the future configuration of /etc/mail/
sendmail.cf files.
24.3.1.4. Masquerading
One common Sendmail configuration is to have a single machine act as a mail gateway for
all machines on the network. For instance, a company may want to have a machine called
mail.example.com that handles all of their email and assigns a consistent return address to all
outgoing mail.
In this situation, the Sendmail server must masquerade the machine names on the company network
so that their return address is user@example.com instead of user@host.example.com.
To do this, add the following lines to /etc/mail/sendmail.mc:
FEATURE(always_add_domain)dnl
FEATURE(`masquerade_entire_domain')dnl
FEATURE(`masquerade_envelope')dnl
FEATURE(`allmasquerade')dnl
MASQUERADE_AS(`bigcorp.com.')dnl
MASQUERADE_DOMAIN(`bigcorp.com.')dnl
MASQUERADE_AS(bigcorp.com)dnl
After generating a new sendmail.cf using m4, this configuration makes all mail from inside the
network appear as if it were sent from bigcorp.com.
Sendmail
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