Authenticated SMTP with Postfix on CentOS.

#yum install postfix system-switch-mail cyrus-imapd cyrus-plain cyrus-md5 cyrus-utils cyrus-sasl cyrus-sasl-plain cyrus-sasl-md5 dovecot.

#vi /etc/postfix/main.cf

      inet_interfaces = all
      relayhost = smtp.*******.com                             
      smtp_sasl_auth_enable = yes
      smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
      smtp_sasl_mechanism_filter = plain, login                  
      smtp_sasl_security_options = noanonymous       

#vi  /etc/postfix/sasl_passwd

  Place the following line to the file : emailserver username:password  (Our email server)

# postmap /etc/postfix/sasl_passwd

  Restart Service.

# /etc/init.d/saslauthd restart
# /etc/init.d/postfix restart