add short-term workaround for smtp-smuggling

templates/main.cf.j2

@@ -34,6 +34,9 @@ smtp_tls_security_level = {{ postfix.ssl.outgoing_security_level }}
 
 smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
 
+# short-term workaround for https://www.postfix.org/smtp-smuggling.html
+smtpd_data_restrictions = reject_unauth_pipelining
+
 # SMTPD default settings
 smtpd_helo_required = yes
 strict_rfc821_envelopes = yes