Ssmtp with Google

Get an app password from here

Add the following lines to /etc/ssmtp/ssmtp.conf:

root=myusername@gmail.com
mailhub=smtp.gmail.com:465
FromLineOverride=YES
AuthUser=myusername@gmail.com
AuthPass=passwordcreatedfromabove
UseTLS=YES

Send a test email:

echo "Testing...1...2...3" | ssmtp emailaddress@gmail.com

Sending with an attachment

echo -e "to: receiver@domain.tld\nsubject: subject\n"| (cat - && uuencode /path/to/attachment attachment.name) | ssmtp receiver@gmail.com

Notes

apt-get install sharutils to get uuencode command