In case that your SMTP server has authentication (like Gmail), For this purpose we will use Postfix. I

Install the needed packages:

Ubuntu

apt-get install postfix mailutils libsasl2-2 ca-certificates libsasl2-modules

CentOS

yum update && yum install postfix mailx cyrus-sasl cyrus-sasl-plain

• Set Postfix config file /etc/postfix/main.cf. Add this lines to the end of the file:

1. Set Postfix config file /etc/postfix/main.cf. Add this lines to the end of the file:

   Ubuntu

   relayhost = [smtp.gmail.com]:587
   smtp_sasl_auth_enable = yes
   smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
   smtp_sasl_security_options = noanonymous
   smtp_tls_CAfile = /etc/ssl/certs/thawte_Primary_Root_CA.pem
   smtp_use_tls = yes
   

   CentOS

   relayhost = [smtp.gmail.com]:587
   smtp_sasl_auth_enable = yes
   smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
   smtp_sasl_security_options = noanonymous
   smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt
   smtp_use_tls = yes
   

2. Configure email address and password:

   echo [smtp.gmail.com]:587 USERNAME@gmail.com:PASSWORD > /etc/postfix/sasl_passwd
   postmap /etc/postfix/sasl_passwd
   chmod 400 /etc/postfix/sasl_passwd
   

3. Secure DB password

   chown root:root /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
   chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
   

4. Reload Postfix

   systemctl reload postfix

• Test you configuration with:

  echo "Test mail from postfix" | mail -s "Test Postfix" you@example.com
  echo "Test mail from postfix" | mail -s "Test Postfix" -r someone@whatever.com you@example.com (this is if your reply address has to come from a specific sender)
  

  You should receive an email on you@example.com

You should receive an email on you@example.com

Note: If you are using centos 7, which uses systemD. You will find that postfix doesn’t send maillogs to /var/log/maillog. Someone decided it would be a great idea to send it to the journaler instead.…

In order to find your mail logs and or tail the logs for postfix.

• Journalctl -u postfix (view all logs)
• Journalctl -u postfix -f (to tail the mail logs)