In case anyone else ever has this problem, the solution as it turned out was a simple one—I just needed to add a ‘machine’ entry in DNS for the WAN port (10.1.10.2).
In Server Admin, I went to DNS>Settings and clicked on my zone (jcfoffice.org). I then clicked on ‘Machines’. I added a new machine with the same name as the original server but the IP of the WAN port (10.1.10.2).
Voilà.
A week of work and it all came to that. 🙄