Using gmail as a relay

apt-get install libsasl2-2 ca-certificates libsasl2-modules
Add this to /etc/postfix/main.cf

# use gmail as a relay
relayhost = [smtp.gmail.com]:587
smtp_use_tls = yes
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/Equifax_Secure_CA.pem

Add something like this to /etc/postfix/sasl_passwd
[smtp.gmail.com]:587 user-name@gmail.com:users-password

postmap /etc/postfix/sasl_passwd
chown 600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db

Relay

To get relay working add domain name to mynetworks

mynetworks = 127.0.0.0/8, 10.0.0.0/24, solar.lan, computerking.ca