I have found nothing about .asp files in the documentation about filters. Can Alkaline index .asp files?

The Active Server Pages (.asp) files are generated by the server. This means that they are entirely preprocessed by your Apache or IIS web server. If the results of the .asp page are plain HTML, Alkaline will treat the page as plain HTML.

To index .asp files you will have to add ExtsAdd=asp to the asearch.cnf file in order for the .asp URLs to be indexed by the spider. You might also need to add Cgi=Y if the asp urls contain parameters such as index.asp?foo&bar .