Put your generated key in
/etc/postfix/certs/freerelay-key.pem, and the certificate you received by email in
/etc/postfix/main.cf and add the following lines:
smtp_use_tls = yes smtp_tls_key_file = /etc/postfix/certs/freerelay-key.pem smtp_tls_cert_file = /etc/postfix/certs/freerelay-cert.pem relayhost = [freerelay.err.no]:2525
After doing that, restart postfix and check that relaying works. Freerelay listens to port 25, 587 (submission), 6667 (irc) and 2525, so if any of those are blocked in your network, try another one.