diff --git a/config/config.inc.php.dist b/config/config.inc.php.dist
--- a/config/config.inc.php.dist
+++ b/config/config.inc.php.dist
@@ -62,7 +62,7 @@
 $config['fileapi_manticore'] = null;
 
 // WOPI/Office service URL. Enables use of collaborative editor supporting WOPI.
-// Note: this URL should be accessible from Chwala host and Roundcube host as well.
+// Note: this URL must be accessible from the Chwala host.
 $config['fileapi_wopi_office'] = null;
 
 // Name of the user interface skin.
@@ -73,6 +73,9 @@
 // the UI location is used with addition of /api/ suffix.
 $config['file_api_url'] = '';
 
+// Optional server variant of file_api_url if the wopi service needs to connect via an internal url back to chwala.
+$config['file_api_server_url'] = null;
+
 // Type of Chwala cache. Supported values: 'db', 'apc' and 'memcache'.
 // Note: This is only for some additional data like WOPI capabilities.
 $config['fileapi_cache'] = 'db';
diff --git a/lib/file_wopi.php b/lib/file_wopi.php
--- a/lib/file_wopi.php
+++ b/lib/file_wopi.php
@@ -97,8 +97,10 @@
             return;
         }
 
-        $office_url  = rtrim($metadata['urlsrc'], ' /?'); // collabora
-        $service_url = $this->api->api_url() . '/wopi/files/' . $id;
+        $office_url = rtrim($metadata['urlsrc'], ' /?'); // collabora
+        //Configurable if e.g. collabora does not connect via the public url
+        $service_url = $this->rc->config->get('file_api_server_url', $this->api->api_url());
+        $service_url = rtrim($service_url, ' /') . '/wopi/files/' . $id;
 
         // @TODO: Parsing and replacing placeholder values
         // https://wopi.readthedocs.io/en/latest/discovery.html#action-urls