This will make network configuration and host based authentication
more robust, across different deployment platforms.
The options `RELAYNETS` and`POD_ADDRESS_RANGE` are kept for compatibility.
However, their usage have become optional.
To facilitate this, the default redirect at / can be disabled, even if
the default remains at redirecting to the webmailer.
The extensions are within the host scope and are read from
$ROOT/overrides/nginx/*.conf.
Tim Möhlmann