sudo aptitude install ssmtp

sudo vim /etc/ssmtp/ssmtp.conf

root=username@gmail.com
mailhub=smtp.gmail.com:587
hostname=username@gmail.com
UseSTARTTLS=YES
AuthUser=username
AuthPass=password
FromLineOverride=yes

mailutils libsasl2-2 ca-certificates libsasl2-modules

sudo vim /etc/postfix/main.cf

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/postfix/cacert.pem
smtp_use_tls = yes

vim /etc/postfix/sasl_passwd

[smtp.gmail.com]:587    USERNAME@gmail.com:PASSWORD

vim /etc/mail/access

To:a1@server.vikas.com        REJECT            # Reject a1 user from recieving mails
From:a1@server.vikas.com     REJECT           # Reject a1 user from sending mails

root:       example@gmail.com