Substitute variables properly in dovecot configuration

dovecot/start.sh

@@ -1,4 +1,9 @@
-#!/bin/sh
+#!/bin/bash
+
+# Substitute configuration
+for VARIABLE in `env | cut -f1 -d=`; do
+  sed -i "s={{ $VARIABLE }}=${!VARIABLE}=g" /etc/dovecot/*.conf
+done
 
 # Fix permissions
 chown -R mail:mail /mail