mosConfig_mailfrom

if ( defined( 'JPATH_ADMINISTRATOR' ) ) {
$app = &JFactory::getApplication();
$mosConfig_sitename=$app->getCFG('sitename');
$mosConfig_mailfrom=$app->getCFG('mailfrom');
$mosConfig_fromname=$app->getCFG('fromname');

mosConfig_mailfrom contains value in mailfrom variable defined in configuration.php in root install folder of joomla