sSMTP is alternative to Sendmail.  sSMTP is a send-only sendmail emulatorfor machines which normally pick their mail up from a centralized mailhub (viapop, imap, nfs mounts or other means). It provides the functionality requiredfor humans and programs to send mail via the standard or /usr/bin/mail useragents. It is used to send mail to externalemail address after authentication with valid mail account.
Download & Install
# rpm -Uvh 
# yum -y install ssmtp
Now we will editthe ssmtp configuration file. 
# cd /etc/ssmtp
# vim /etc/ssmtp/ssmtp.conf
Here is the custom configuration         # SMTP server hostname and port
UseTLS=NO                             # Secure connection (SSL/TLS)
FromLineOverride=YES                  # Force the From: line           # The name of this host      # The host the mail appears to be coming from
Root=Bala                             # Redirect mail for root@ to postmaster@           # Your DreamHost mailaccount
AuthPass=myemailpassword              # The password for the mail account
Now let’sconfigure the Aliases
# vim /etc/ssmtp/revaliases
If you would like to change the “FromDisplay Name, edit the /etc/passwd and modify theuser alias
# vim /etc/passwd 
Before we start using sSMTP lets stop thesendmail which is default installed on all Linux distribution.Stop sendmailservice to start after reboot
# service sendmail stop
# sudo chkconfig –levels 2345 sendmail off
Move or replace the sendmail and thencreate
a symbolic link for sSMTP to sendmail with authentication
# mv /usr/sbin/sendmail/usr/sbin/sendmail.orig
# ln -s /usr/sbin/ssmtp/usr/sbin/sendmail
We all done with the installation andconfiguration let’s send a test mail to internal & external email addressusing sSMTP. 

echo”Sending Test mail to external & Internal email address”| mail -s”This is the test message using sSMTP”

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