Initially I just had a FE and a BE box and that is working great. The FE box is in the DMZ, which runs OWA and RPC over HTTP.
I have installed a 2nd BE box, and have set it up just like the 1st BE box. Problem being is authentication to the 2nd box via pop3/smtp/rpc over http won’t work. But if I use webmail, I can login and view e-mail.