diff --git a/README.md b/README.md
index b9a015f..a175365 100644
--- a/README.md
+++ b/README.md
@@ -36,6 +36,9 @@ The following env variables need to be passed to the container:
 The following env variable(s) are optional.
 * `SMTP_HEADER_TAG` This will add a header for tracking messages upstream. Helpful for spam filters. Will appear as "RelayTag: ${SMTP_HEADER_TAG}" in the email headers.
 
+* `SMTP_NETWORKS` Setting this will allow you to add additional, comma seperated, subnets to use the relay. Used like
+    -e SMTP_NETWORKS='xxx.xxx.xxx.xxx/xx,xxx.xxx.xxx.xxx/xx'
+
 To use this container from anywhere, the 25 port or the one specified by `SMTP_PORT` needs to be exposed to the docker host server:
 
     docker run -d --name postfix -p "25:25"  \ 
diff --git a/run.sh b/run.sh
index b672c67..247971e 100644
--- a/run.sh
+++ b/run.sh
@@ -51,5 +51,19 @@ if [ ! -z "${SMTP_HEADER_TAG}" ]; then
   echo "Setting configuration option SMTP_HEADER_TAG with value: ${SMTP_HEADER_TAG}"
 fi
 
+#Check for subnet restrictions
+nets='10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16'
+if [ ! -z "${SMTP_NETWORKS}" ]; then
+        for i in $(sed 's/,/\ /g' <<<$SMTP_NETWORKS); do
+                if grep -Eq "[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}/[0-9]{1,2}" <<<$i ; then
+                        nets+=", $i"
+                else
+                        echo "$i is not in proper IPv4 subnet format. Ignoring."
+                fi
+        done
+fi
+add_config_value "mynetworks" "${nets}"
+
+
 #Start services
 supervisord