The list I tried to unsubscribe from is about Debian not gnumeric, Steve
I just unsubscribed and resubscribed, it seems to work for me.
Here's what I did:
1. Go to the gnumeric mailman page:
https://mail.gnome.org/mailman/listinfo/gnumeric-list
2. Enter the email address you get the gnumeric mails on in the box
near the bottom (under "gnumeric-list Subscribers")
3. Click "Unsubscribe or Edit Options"
4. Click "Unsubscribe". A message appears: "A confirmation email has been sent".
5. An email will arrive containing an unsubscribe link. Click the link.
6. On the unsubscribe page, click "Unsubscribe".
You may have to enter your password at various points. Your browser
will probably do it for you. You also need to have cookies enabled.
John