[Haskell-cafe] subscription problems for projects.haskell.org mailing list

Hello, I created a mailing list for Grapefruit on the Haskell Community Server (<grapefruit@projects.haskell.org>). If I try to subscribe to it, I receive a confirmation e-mail but my answers to this e-mail seem to get ignored. Does anyone have an idea what’s wrong here? Best wishes, Wolfgang