By default configured to accept connection from local system (127.0.0.1). This should avoid open mail relay problem.
To allow connections from ALL hosts/LAN IPs open sendmail.mc file (login as the root):
# vi /etc/mail/sendmail.mc
Look for line that read as follows:
Comment or remove above line and insert new line that read as follows:
Above line will force to accept connection from any host. Save the file. Regenerate sendmail configuration file using m4:
# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
If this command is resulting by giving such of error as below, this means that the file
/etc/mail/sendmail.mc:10: m4: cannot open `/usr/share/sendmail-cf/m4/cf.m4': No such file or directory
Then, this means that the sendmail.cf.xx rpm package is missing and require to be installed.
In my case, I had to mount the cdrom, and look for this rpm file:
Restart sendmail service :
# /etc/init.d/sendmail restart