Postfix Remote Client Relay

["Gene Grimm" <elessar@noi.net>]

We are trying to configure our new Postfix mail server to allow relay for a
new remote client. Our configuration file currently includes the following
directive in main.cf:

smtpd_client_restrictions = permit_mynetworks,
        check_client_access hash:/etc/postfix/client_access,
        reject_unknown_client

All the remaining 'smtpd_' directives are default. The mail.log file shows
the attempt to send mail that should have been permitted.

Feb  1 10:17:23 mail-gr-oh postfix/smtpd[19051]: connect from
unknown[207.17.252.3]
Feb  1 10:17:23 mail-gr-oh postfix/smtpd[19051]: 87555337E2:
client=unknown[207.17.252.3]
Feb  1 10:17:23 mail-gr-oh postfix/smtpd[19051]: reject: RCPT from
unknown[207.17.252.3]: 554 <gag@networksonline.com>: Recipient address
rejected: Relay access denied; from=<allison@caaofcc.org>
to=<gag@networksonline.com>
Feb  1 10:17:29 mail-gr-oh postfix/smtpd[19051]: disconnect from
unknown[207.17.252.3]

What configuration do we need to permit a specific external IP address to
relay from outside our network to any recipients without opening the server
for spammers?

Any guidance on this would be appreciated.