There are two Digger mailing lists, one to receive information about new versions and one to chat about Digger, swap DRFs etc. Note that updates are sent to the Chat mailing list as well as the update list, so there's no need to subscribe to both.
To subscribe to the Digger Update mailing list, go here and sign up. To subscribe to the Digger Chat mailing list, go here and sign up. To unsubscribe or change your settings (for either list), you need to click here and login.
The archives from the old Digger Chat mailing list (which was destroyed due to a misunderstanding) are available at the download page.