Install

sudo apt-get install ssmtp mailutils

Configure

edit file sudo nano /etc/ssmtp/ssmtp.conf

root=username@gmail.com
mailhub=smtp.gmail.com:465
rewriteDomain=gmail.com
AuthUser=username
AuthPass=password
FromLineOverride=YES
UseTLS=YES

Test

ssmtp recipient@gmail.com < text.txt

mail -s "test" recipient@gmail.com < text.txt