Have you tried subscribing directly from the scala website?
http://www.scala-lang.org/node/199Related to Grails: There is a note at the bottom of this page:
http://grails.org/Mailing+lists ("If you have trouble subscribing via email you can go to
http://xircles.codehaus.org/manage_email and register an e-mail to subscribe."). In any case, you should contact the mailing list owner.