Hi Winan,

If your still using Red Hat Linux 7.2 then the following from the HOWTO should work for you. You would need to edit your /etc/mail/access file.

The access file is aptly named as its purpose is to control access to
the sendmail daemon.  It is used both to allow and deny relay access.  Here
are some examples of what the file's entries may look like:

localhost.localdomain   RELAY
localhost               RELAY
127.0.0.1               RELAY
192.168.1.1             RELAY
10.0.0.6                RELAY
baddomain.net           550 Mail from your domain is denied
192.168.1.10            550 Internet mail may not be sent from this host.

LelandJ