You can definitly tune your postfix to accept specific EHLO clients or IPs without authentication.
Create a /etc/postfix/helo_client_exceptions file with
mail.example.org        PERMIT
XX.XX.XX.XX			PERMIT
Postmap that file with $ /etc/postfix/helo_client_exceptions
Add it to your /etc/postfix/main.cf file in the smtpd_relay_restrictions section.
Example, here’s mine, you probably won’t need all those arguments
smtpd_relay_restrictions =
        permit_mynetworks,
        permit_sasl_authenticated,
        check_client_access hash:/etc/postfix/helo_client_exceptions,
        check_sender_access hash:/etc/postfix/sender_checks,
        # This list restricts recipients when client has no authentication
        #check_recipient_access hash:/etc/postfix/recipient_checks,
        reject_unauth_destination,
        reject_invalid_hostname,
        ### Can cause issues with Auth SMTP, so be weary!
        reject_non_fqdn_hostname,
        ###  Basic antispam
        reject_non_fqdn_sender,
        reject_non_fqdn_recipient,
        reject_unknown_sender_domain,
        reject_unknown_recipient_domain,
        reject_unknown_client_hostname,
        permit_mynetworks,
        reject_unauth_destination,
        check_client_access
        hash:/etc/postfix/rbl_client_exceptions,
        # Aug 2018: sorbs is a bit too harsh, blocks legit IPs (gmail, orange, github...)
        #reject_rbl_client dnsbl.sorbs.net,
        reject_rbl_client cbl.abuseat.org,
        #reject_rbl_client sbl-xbl.spamhaus.org,
        reject_rbl_client zen.spamhaus.org,
        reject_rbl_client bl.spamcop.net,
        reject_rbl_client b.barracudacentral.org,
        reject_rhsbl_sender    dsn.rfc-ignorant.org,
        permit
Reload your postfix with systemctl reload postfix and voilà ;)