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

• Put to /etc/postfix/sasl/sasl_passwd the login data of the SMTP host:

[smtp.example.net]:587 username:password

• # postmap /etc/postfix/sasl/sasl_passwd
• Put your SMTP host address to /etc/postfix/sender_canonical_maps:

/.+/    user@example.net

• # postmap /etc/postfix/sender_canonical_maps
• Add something like

root:           user
user:           user@example.org

to the end of /etc/aliases; then run the command newaliases

• # /etc/rc.d/rc.postfix restart