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 ;)