diff --git a/Dockerfile b/Dockerfile
index 373900c..758002d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -68,9 +68,7 @@ RUN postconf -e non_smtpd_milters=inet:opendkim:8891
 RUN postconf -e milter_default_action=accept
 RUN postconf -e milter_protocol=6
 RUN postconf -e virtual_alias_maps=lmdb:/etc/postfix/maps/virtual
-RUN postconf -e sender_canonical_maps=tcp:postsrsd:10001
 RUN postconf -e sender_canonical_classes=envelope_sender
-RUN postconf -e recipient_canonical_maps=tcp:postsrsd:10002
 RUN postconf -e recipient_canonical_classes=envelope_recipient,header_recipient
 RUN postconf -e smtpd_client_connection_rate_limit=10
 
diff --git a/postfixd.sh b/postfixd.sh
index 93026e3..bb653cb 100755
--- a/postfixd.sh
+++ b/postfixd.sh
@@ -13,6 +13,11 @@ case $1 in
       postconf -e non_smtpd_milters="${MILTERS}"
     fi
 
+    if test -n "${SRS}"; then
+      postconf -e sender_canonical_maps=tcp:${SRS}:10001
+      postconf -e recipient_canonical_maps=tcp:${SRS}:10002
+    fi
+
     test -n "${NETWORKS}" && postconf -e mynetworks="${NETWORKS}"
 
     ;;