Postfix as a send-only SMTP relay
# mkdir -p /etc/postfix/sasl- Add the following parameters to the end of
/etc/postfix/main.cf:
myhostname = localhost.example.com inet_interfaces = loopback-only mynetworks = 127.0.0.0/8 relayhost = [smtp.example.net]:587 smtp_sasl_auth_enable = yes smtp_sasl_security_options = noanonymous smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd smtp_tls_security_level = may smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt sender_canonical_maps = regexp:/etc/postfix/sender_canonical_maps