John,I see you are using Thunderbird as am I. Assuming your using the 2 pane view with the preview pane, you can easily click the drop down + just to the left of the subject to reveal additional header information and you should see the list's debian-user@lists.debian.org address.. You should then be able to click the address and choose Compose mail to option. Additionally you could add the list as a contact.
Daryl