diff --git a/mailsrv/assets/postfix/main.cf.part b/mailsrv/assets/postfix/main.cf.part
index b6279b1..f1b0cc3 100644
--- a/mailsrv/assets/postfix/main.cf.part
+++ b/mailsrv/assets/postfix/main.cf.part
@@ -56,7 +56,7 @@ smtpd_sasl_auth_enable = yes
 smtpd_delay_reject = yes
 smtpd_helo_required = yes
 # reject hosts with malformed identifiers
-smtpd_helo_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_invalid_helo_hostname, reject_non_fqdn_helo_hostname, reject_unknown_helo_hostname
+smtpd_helo_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_invalid_helo_hostname, reject_non_fqdn_helo_hostname, reject_unknown_reverse_client_hostname
 # reject hosts that improperly use SMTP commands
 smtpd_data_restrictions = reject_unauth_pipelining
 # reject unauthorized relay attempts