issue warning in case of improper restart (#3129)

docs/content/usage.md

@@ -58,6 +58,8 @@ chmod a+x ./setup.sh
 
     **Use `docker compose up / down`, not `docker compose start / stop`**. Otherwise, the container is not properly destroyed and you may experience problems during startup because of inconsistent state.
 
+    Using `Ctrl+C` **is not supported either**!
+
 You are able to get a full overview of how the configuration works by either running:
 
 1. `./setup.sh help` which includes the options of `setup.sh`.

target/scripts/start-mailserver.sh

@@ -33,6 +33,7 @@ function _register_functions
 
   # ? >> Checks
 
+  _register_check_function '_check_improper_restart'
   _register_check_function '_check_hostname'
   _register_check_function '_check_log_level'
 

target/scripts/startup/check-stack.sh

@@ -17,6 +17,17 @@ function _check
   done
 }
 
+function _check_improper_restart
+{
+  _log 'debug' 'Checking for improper restart'
+
+  if [[ -f /CONTAINER_START ]]
+  then
+    _log 'warn' 'This container was (likely) improperly restarted which can result in undefined behavior'
+    _log 'warn' 'Please destroy the container properly and then start DMS again'
+  fi
+}
+
 function _check_hostname
 {
   _log 'debug' 'Checking that hostname/domainname is provided or overridden'