diff --git a/.env.example b/.env.example
index 0099c2b..ea1d35c 100644
--- a/.env.example
+++ b/.env.example
@@ -37,3 +37,6 @@
 
 # Optional: This will disable (no) or enable (yes) the use of SMTPUTF8
 #SMTPUTF8_ENABLE=no
+
+# Optional: This will use allow you to set a custom $message_size_limit value. Default is 10240000.
+#MESSAGE_SIZE_LIMIT=
diff --git a/README.md b/README.md
index bb12228..dbab175 100644
--- a/README.md
+++ b/README.md
@@ -83,6 +83,8 @@ The following env variable(s) are optional.
 
 * `SMTPUTF8_ENABLE` This will enable (default) or disable support for SMTPUTF8. Valid values are `no` to disable and `yes` to enable. Not setting this variable will use the postfix default, which is `yes`.
 
+* `MESSAGE_SIZE_LIMIT` This will change the default limit of 10240000 bytes (10MB).
+
 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 a731e8b..6f540ca 100644
--- a/run.sh
+++ b/run.sh
@@ -99,6 +99,12 @@ if [ ! -z "${OVERWRITE_FROM}" ]; then
   echo "Setting configuration option OVERWRITE_FROM with value: ${OVERWRITE_FROM}"
 fi
 
+# Set message_size_limit
+if [ ! -z "${MESSAGE_SIZE_LIMIT}" ]; then
+  postconf -e "message_size_limit = ${MESSAGE_SIZE_LIMIT}"
+  echo "Setting configuration option message_size_limit with value: ${MESSAGE_SIZE_LIMIT}"
+fi
+
 #Start services
 
 # If host mounting /var/spool/postfix, we need to delete old pid file before