Sendmail is only accepting connections from localhost

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:

DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

Comment or remove above line and insert new line that read as follows:

DAEMON_OPTIONS(`Port=smtp,Name=MTA')dnl

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:

sendmail-cf-8.13.8-2.el5.i386.rpm

Restart sendmail service :

# /etc/init.d/sendmail restart