Configuring Sendmail RedHat /CentOS/Fedora

Configuring it is very simple. First you'll need the sendmail-cf package. Install it using yum:

[root@mail-server ~]# yum install sendmail-cf

Edit the file /etc/mail/sendmail.mc and add the following lines. Make sure you set your mail server domain name where it's bolded:

MASQUERADE_AS(yourdomain.com)dnl
MASQUERADE_DOMAIN(yourdomain.com)dnl

In the same file /etc/mail/sendmail.mc remove the "dnl" from the beginning of the lines so it will look like this:

LOCAL_DOMAIN(`localhost.localdomain')dnl
FEATURE(masquerade_envelope)dnl
FEATURE(masquerade_entire_domain)dnl

Save the file and compile it using m4:

[root@mail-server ~]# m4 /etc/mail/sendmail.mc > /etc/sendmail.cf

Send Sendmail a -HUP signal using kill or simply restart the daemon for the configuration changes to take effect:

[root@mail-server ~]# service sendmail restart

Testing your configuration using sendmail

And that's it! you're done. Just send yourself a test email to make sure it is really working:

[root@mail-server ~]# /usr/sbin/sendmail -t < mail.txt

Where the contents of the mail.txt file are:

Date: Wed Dec 1 08:41:54 2010
To: you@somewhere.com
Subject: The subject of the message
From: whatever@somewhere.com Body of message goes here

Testing your configuration using mutt

You can also use mutt to test, which is a bit simpler (and you can also add the -a parameter for file attachment):

[root@mail-server ~]# mutt -s "Test Email" you@somewhere.com < /dev/null