Unfortunately, the university mailman server was being decommissioned and the Wekalist had to find a new home. Its home is now on Sourceforge.net, where all the Weka releases and packages are hosted as well:

https://sourceforge.net/projects/weka/lists/weka-users

You can find the mailing list archives here from now on:

https://sourceforge.net/p/weka/mailman/weka-users/

Due to the move, you will have to subscribe again before you can post to the list using the following email address:

weka-users@lists.sourceforge.net