Sometime Today, Mayank Sarup assembled some asciibets to say:
Open your sendmail.cf and look for a line Addr or something.
No, don't do that. Don't edit sendmail.cf at any cost. Only edit /etc/mail/sendmail.mc, and use that to regenerate sendmail.cf.
Basically, you'll find a line that tells sendmail to act as an MTA only for localhost (127.0.0.1) (same as what mayank said), you should comment it out there, and then use:
m4 /etc/mail/sendmail.mc > /etc/sendmail.cf
to regenerate sendmail.cf. If you want to be safe, write the output to a different file, and then copy it over sendmail.cf
I'll give more complete instructions on Monday when I have access to a later version of sendmail.cf. At home I have 8.9.3
Basically, Red Hat in its infinite wisdom runs sendmail only on localhost/127.0.0.1 to enhance security. (Postfix/qmail way better).
Why is everyone so much against redhat? This just loses the point of open source - that it gives you so much choice. If you don't like redhat, use something else.
There is a very good reason for redhat binding sendmail only as a local mta.
The average user would not be running a mail server, and therefore would not know how to protect himself against mail relay. He only needs sendmail to queue mails while he's offline. Sendmail is not required to receive mails from your ISP.
If someone did require to set up a mail server, then it should be required that that person know how to set up a mailserver. In that case, he should know how to enable relay, OR, how to uninstall sendmail, and install the MTA of his choice.
RedHat's policy simply ensures that casual users don't hurt themselves, and that people who claim to be mailadmins actually know their job.
Philip