diff --git a/install_postfix_advanced.sh b/install_postfix_advanced.sh
index ea85bdc..832970c 100755
--- a/install_postfix_advanced.sh
+++ b/install_postfix_advanced.sh
@@ -171,8 +171,10 @@ fi
 if [[ -z "$_RELAY_HOST" ]]; then
    _IS_RELAY_HOST=$DEFAULT_IS_RELAY_HOST
 else
-   _IS_RELAY_HOST="$_RELAY_HOST"
+   _IS_RELAY_HOST="${_RELAY_HOST,,}"
 fi
+[[ "${_IS_RELAY_HOST}" == "yes" ]] && _IS_RELAY_HOST=true
+[[ "${_IS_RELAY_HOST}" == "no" ]] && _IS_RELAY_HOST=false
 
 if [[ -z "$_LISTEN_ON_ADDITIONAL_RELAY_PORT" ]] ; then
    _LISTEN_ON_ADDITIONAL_RELAY_PORT=${DEFAULT_LISTEN_ON_ADDITIONAL_RELAY_PORT}