apt-get install ssmtp mailutils

rm -r /etc/ssmtp/ssmtp.conf
nano /etc/ssmtp/ssmtp.conf


GMAIL CONFIG
***********************************************

# The user that gets all the mails (UID < 1000, usually the admin)
root=noreply@xxxxxxxxxxxxxxx

# The mail server (where the mail is sent to), both port 465 or 587 should be acceptable
# See also https://support.google.com/mail/answer/78799
mailhub=smtp.gmail.com:587

# The address where the mail appears to come from for user authentication.
rewriteDomain=gmail.com

# The full hostname
hostname=localhost

# Use SSL/TLS before starting negotiation
UseTLS=Yes
UseSTARTTLS=Yes

# Username/Password
AuthUser=xxxxxxxxxxxxxxxxxxxxx
AuthPass=xxxxxxxxxxxxxx
AuthMethod=LOGIN

# Email 'From header's can override the default domain?
FromLineOverride=yes

***********************************************




add
root:xxxxx@gmail.com:smtp.gmail.com:587
youruser:xxxxxx@gmail.com:smtp.gmail.com:587





******IMPORTANT****
send-mail: Authorization failed

Take the step mentioned earlier.
Log into your google email account and then go to this link: https://www.google.com/settings/security/lesssecureapps and set "Access for less secure apps" to ON.
Test to see if your issue is resolved. If it isn't resolved, as it wasn't for me, continue to Step #2.

https://accounts.google.com/b/0/DisplayUnlockCaptcha

echo test | mail -v -s "testing ssmtp setup" xxxxxxxxxxxxx@gmail.com