Resolve healthcheck issues around domain splitting with an index route

app.py

@@ -7,6 +7,10 @@ env = jinja2.Environment(
     autoescape=jinja2.select_autoescape(['xml'])
 )
 
+@app.route('/')
+def index():
+    return "Mail Autoconfig Service is running."
+
 @app.route('/mail/config-v1.1.xml')
 def thunderbird_config():
     domain = request.host.split('.', 1)[1]