Setting up SMTP email notifications in FreePBX can't be set up from the UI without the commercial 'System Admin' module. The good news is, it can be set up manually with hardly any fuss!
Email Setup
SSH into the system
Edit '/etc/postfix/main.cf'
Edit '/etc/postfix/sasl_passwd'
Force postfix to rewrite from address, inside '/etc/postfix/generic'
To rewrite the domain for all addresses from the local pbx, use this format in '/etc/postfix/generic':
Set permissions 'chmod 400 /etc/postfix/sasl_passwd'