diff --git a/target/postfix/main.cf b/target/postfix/main.cf
index 1ce6b261..f64aefa3 100644
--- a/target/postfix/main.cf
+++ b/target/postfix/main.cf
@@ -50,7 +50,7 @@ smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname, permi
 smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
 smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination, check_policy_service unix:private/policyd-spf, reject_unauth_pipelining, reject_invalid_helo_hostname, reject_non_fqdn_helo_hostname, reject_unknown_recipient_domain, reject_rbl_client zen.spamhaus.org
 smtpd_client_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination, reject_unauth_pipelining
-smtpd_sender_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unknown_sender_domain
+smtpd_sender_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unknown_sender_domain, reject_unknown_client_hostname
 disable_vrfy_command = yes
 
 # Postscreen settings to drop zombies/open relays/spam early