diff --git a/target/postfix/main.cf b/target/postfix/main.cf
index 495ad8a9..8c1d4c89 100644
--- a/target/postfix/main.cf
+++ b/target/postfix/main.cf
@@ -68,6 +68,7 @@ smtpd_forbid_bare_newline = yes
 # smtpd_forbid_bare_newline_exclusions = $mynetworks
 
 # Custom defined parameters for DMS:
+# reject_unknown_sender_domain: https://github.com/docker-mailserver/docker-mailserver/issues/3716#issuecomment-1868033234
 dms_smtpd_sender_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unknown_sender_domain
 # Submission ports 587 and 465 support for SPOOF_PROTECTION=1
 mua_sender_restrictions = reject_authenticated_sender_login_mismatch, $dms_smtpd_sender_restrictions